Acute autonomic neuropathy. Two cases and a clinical review. Acute autonomic neuropathy is an uncommon syndrome, usually affecting healthy young people. Presentation is often dramatic and initial misdiagnosis is common. We describe two young women with acute autonomic neuropathy who presented with gastrointestinal involvement heralding widespread dysautonomia and review 26 additional cases of acute autonomic neuropathy from the English language literature. Acute autonomic neuropathy can be primarily cholinergic without orthostatic hypotension (26%) or pandysautonomic (74%) involving sympathetic adrenergic functions. Onset has been temporally related to viral syndromes in 20% of cases, with autonomic deficits usually evolving over 1 to 3 weeks. Gastroparesis (69%) and syncope (12%) are frequent presenting complaints. Spinal fluid protein levels are often (75%) elevated in pandysautonomic subtypes. Prolonged and incomplete recovery is the rule (60%), with persistent gastroparesis and orthostatic hypotension. Other specific diseases that occasionally mimic acute autonomic neuropathy include botulism, porphyria, amyloidosis, and paracarcinomatous neuropathies. Acute autonomic neuropathy shares several clinical features with acute idiopathic polyneuropathy (Guillain-Barre syndrome), suggesting an immune-mediated pathogenesis. 