This is a small Accipiter hawk, with males 23 to 30 cm (9.1 to 11.8 in) long, with a wingspan of 42 to 58 cm (17 to 23 in) and weight from 82–115 g (2.9–4.1 oz).
As common in Accipiter hawks, females are distinctly larger in size, averaging some 30% longer, and with a weight advantage of more than 50% being common.
The female measures 29 to 37 cm (11 to 15 in) in length, has a wingspan of 58 to 68 cm (23 to 27 in) and weighs 150 to 219 g (5.3 to 7.7 oz).
The wings measure 14.1–22.9 cm (5.6–9.0 in) each, the tail is 12–19 cm (4.7–7.5 in) long and the tarsus is 4.5–5.9 cm (1.8–2.3 in).
Measurements given here are for the northern group, but they are comparable for the remaining subspecies.
Adults have short broad wings and a medium-length tail banded in blackish and gray with the tip varying among individuals from slightly notched through square to slightly rounded (often narrowly tipped white).
The remiges (typically only visible in flight) are whitish barred blackish.
The legs are long and very slender (hence the common name) and yellow.
The hooked bill is black and the cere is yellowish.
The remaining plumage varies depending on group:
Nominate group: Cap dark and upperparts blue-grey (the former darker).
Often, a few more-or-less random white spots can be seen on the scapulars (feathers attached to the wing that cover the meeting of wing and body).
Underparts white with rufous or tawny bars.
The crissum (the undertail coverts surrounding the cloaca) is white.
Thighs rufous, but often barred white.
The cheeks are tinged rufous (sometimes faint, but generally very distinct in taxa from the Greater Antilles).
The irides are dark orange to red, but these are yellowish to pale orange in juveniles.
Juveniles have dark brownish upperparts, each feather edged rufous, giving a rather scaly appearance.
The brown head is streaked whitish, and the whitish underparts are extensively streaked brown or reddish and usually with reddish barring on the sides.

A. (s.) chionogaster (white-breasted hawk): Resembles the members of the nominate group, but upperparts darker (often appears almost black), thighs whitish-buff and underparts and cheeks entirely white.
Juveniles have darker upperparts and distinctly finer streaking below than juveniles of the nominate group.

A. (s.) ventralis (plain-breasted hawk): Polymorphic.
The most common morph has dark grey upperparts (often appears almost black) and white underparts variably barred, shaded, or mottled with rufous or tawny-buff (extensively marked individuals may appear almost entirely rufous or tawny-buff below).
Occasionally, the barring to the lower belly and flanks may appear duskier.
The white morph has bluish-grey upperparts (similar to the nominate group), but its underparts are all white except for its rufous thighs.
The rare dark morph, the only morph which sometimes lacks rufous thighs, is entirely sooty (occasionally with slight white barring to belly and faint grey bands in tail).
The underparts of the females average paler than males of the same morph.
The iris is typically yellow (contra illustrations in some books), but individuals (mainly sub-adults?)
with a darker iris are occasionally seen.
Juveniles have dark brownish or dusky upperparts with each feather typically edged rufous, giving a rather scaly appearance.
The underparts are white streaked brown, and the thighs are rufous barred white.
Occasionally, juveniles with underparts extensively rufous streaked blackish are seen.

A. (s.) erythronemius (rufous-thighed hawk): Resembles the nominate group, but upperparts darker, streaking to underparts rufous or dusky, cheeks typically with a clear rufous patch (occasionally lacking almost entirely) and iris yellow (contra illustrations in some books).
Juveniles resemble juveniles of the nominate group, but streaking to underparts typically restricted to throat and central underparts, with flanks scaled or barred (often also belly).
This is a small Accipiter hawk, with males 23 to 30 cm (9.1 to 11.8 in) long, with a wingspan of 42 to 58 cm (17 to 23 in) and weight from 82–115 g (2.9–4.1 oz). As common in Accipiter hawks, females are distinctly larger in size, averaging some 30% longer, and with a weight advantage of more than 50% being common. The female measures 29 to 37 cm (11 to 15 in) in length, has a wingspan of 58 to 68 cm (23 to 27 in) and weighs 150 to 219 g (5.3 to 7.7 oz). The wings measure 14.1–22.9 cm (5.6–9.0 in) each, the tail is 12–19 cm (4.7–7.5 in) long and the tarsus is 4.5–5.9 cm (1.8–2.3 in). Measurements given here are for the northern group, but they are comparable for the remaining subspecies. Adults have short broad wings and a medium-length tail banded in blackish and gray with the tip varying among individuals from slightly notched through square to slightly rounded (often narrowly tipped white). The remiges (typically only visible in flight) are whitish barred blackish. The legs are long and very slender (hence the common name) and yellow. The hooked bill is black and the cere is yellowish. The remaining plumage varies depending on group:
Nominate group: Cap dark and upperparts blue-grey (the former darker). Often, a few more-or-less random white spots can be seen on the scapulars (feathers attached to the wing that cover the meeting of wing and body). Underparts white with rufous or tawny bars. The crissum (the undertail coverts surrounding the cloaca) is white. Thighs rufous, but often barred white. The cheeks are tinged rufous (sometimes faint, but generally very distinct in taxa from the Greater Antilles). The irides are dark orange to red, but these are yellowish to pale orange in juveniles. Juveniles have dark brownish upperparts, each feather edged rufous, giving a rather scaly appearance. The brown head is streaked whitish, and the whitish underparts are extensively streaked brown or reddish and usually with reddish barring on the sides.
A. (s.) chionogaster (white-breasted hawk): Resembles the members of the nominate group, but upperparts darker (often appears almost black), thighs whitish-buff and underparts and cheeks entirely white. Juveniles have darker upperparts and distinctly finer streaking below than juveniles of the nominate group.
A. (s.) ventralis (plain-breasted hawk): Polymorphic. The most common morph has dark grey upperparts (often appears almost black) and white underparts variably barred, shaded, or mottled with rufous or tawny-buff (extensively marked individuals may appear almost entirely rufous or tawny-buff below). Occasionally, the barring to the lower belly and flanks may appear duskier. The white morph has bluish-grey upperparts (similar to the nominate group), but its underparts are all white except for its rufous thighs. The rare dark morph, the only morph which sometimes lacks rufous thighs, is entirely sooty (occasionally with slight white barring to belly and faint grey bands in tail). The underparts of the females average paler than males of the same morph. The iris is typically yellow (contra illustrations in some books), but individuals (mainly sub-adults?) with a darker iris are occasionally seen. Juveniles have dark brownish or dusky upperparts with each feather typically edged rufous, giving a rather scaly appearance. The underparts are white streaked brown, and the thighs are rufous barred white. Occasionally, juveniles with underparts extensively rufous streaked blackish are seen.
A. (s.) erythronemius (rufous-thighed hawk): Resembles the nominate group, but upperparts darker, streaking to underparts rufous or dusky, cheeks typically with a clear rufous patch (occasionally lacking almost entirely) and iris yellow (contra illustrations in some books). Juveniles resemble juveniles of the nominate group, but streaking to underparts typically restricted to throat and central underparts, with flanks scaled or barred (often also belly).
Sharp-shinned hawk