Background. Adult T-cell leukemia/lymphoma (ATL) is a severe disease caused by HTLV-I. This paper describes the clinicopathological and immunohistochemical findings of 52 cases of ATL with skin involvement and investigates whether there is any relationship between median survival time (MST) and histological patterns, primary cutaneous involvement and CD8 positivity. Material and methods. All cases were HTLV-I and HIV- and were clinically classified. HTLV-I proviral integration was investigated in atypical cases. Immunohistochemistry was performed using CD3, CD4, CD5, CD7, CD8, CD20, CD25, CD30 and CD45RO markers. Ki-67 was used to evaluate the proliferative index. Results. Twentyseven cases were primary, while 25 were secondary. Monoclonal viral integration was demonstrated in all atypical cases. Patterns resembling mycosis fungoides (MF) were found in 19 cases and anaplastic large-cell lymphoma (ALCL) in two cases. Fifteen cases had an atypical immunophenotype and expressed CD8. Primary cutaneous ATL had a longer MST (48 months) than the secondary cutaneous ATL (7 months) and the difference was statistically significant, but no statistically significant difference was found between the MST of CD8-positive and negative cases. Conclusions. It is important to differentiate between primary and secondary cutaneous ATL and classify the cases histologically in order to better evaluate the prognosis. The two forms of primary cutaneous ATL, primary cutaneous smoldering and primary cutaneous tumoral (PCT), should also be identified. The smoldering type presented a longer survival (58 months) and histological aspects suggestive of better prognosis in contrast to the PCT type that had a shorter survival (20 months) and histological characteristics suggestive of worse outcome.