Cutaneous manifestations of postthymic T cell malignancies: description of five clinicopathologic subtypes. This study was undertaken to identify the cutaneous manifestations among different prognostic subgroups of postthymic T cell malignancies. Cutaneous involvement was demonstrated in 43 of 88 cases. We recognized five clinicopathologic subtypes: type I, classical cutaneous T cell lymphoma (CTCL) or mycosis fungoides, six cases; type II, primary large cell type CTCL, Ki-1 antigen (Ki-1+ or Ki-1-), seven cases; type III, primary angioinvasive T cell lymphoma, three cases; type IV, human T-lymphotropic virus type I (HTLV-I+) adult T cell leukemia/lymphoma (ATL), eight cases; type V, secondary cutaneous involvement by peripheral T cell lymphoma (PTL), 19 cases. Primary CTCL and ATL tend to involve papillary dermis with or without epidermotropism, whereas PTL and angioinvasive T cell lymphoma predominantly affect skin adnexae, vessels, and subcutis. Cutaneous lesions in type V PTL are heterogeneous and may be confused with panniculitis, vasculitis, or an eczematous eruption. Classic CTCL, Ki-1+ lymphoma, and angioinvasive T cell lymphoma have a chronic course, whereas ATL, Ki-1- large cell lymphoma, and PTL are clinically aggressive. 