Peripheral T-cell lymphoma is the most common type of T-cell lymphoma seen in adults in the United States. Clinical data were reviewed from 134 cases of peripheral T-cell lymphoma diagnosed in three centers. The median age of the patients was 57 years (range, 4-97 years), 59% were male, and 36 patients (27%) had a history of a preceding disorder of the immune system. The tumors were grouped histologically into large cell (43%), mixed large and small cell (40%), and small cell (17%). The stage at diagnosis was I (7%), II (21%), III (22%), and IV (50%). B symptoms were present in 57%. The most frequent sites of extranodal involvement were bone marrow (35%), skin (13%), and lung (11%). Eighty patients were treated with a multiagent chemotherapy regimen with proven curative potential in aggressive non-Hodgkin's lymphomas and the remainder of the patients received less intensive chemotherapy (36 patients), radiotherapy (nine patients), or no treatment (nine patients). Fifty percent of the intensively treated patients achieved complete remission and the actuarial 4-year survival was 45%. However, the 4-year, disease-free survival in patients with Stage IV disease was only 10%. Although peripheral T-cell lymphomas appeared similar in many ways to their B-cell counterparts, disease-free survival by stage was low and patients with Stage IV disease had an especially poor outlook.