Twenty-nine cases of adult T-cell leukemia were classified into four types according to the clinical features and course: smoldering, chronic, crisis, and acute. Only 2 of 14 patients with the acute type responded to therapy. The four types showed apparent differences in clinical features, complications, and prognosis, suggesting the need for different therapeutic regimens. For smoldering and chronic cases, no chemotherapy is recommended. However, in crisis and acute cases, aggressive chemotherapy is necessary, although the acute type cases showed extremely poor prognosis despite the most aggressive chemotherapy.