Adult T-cell leukemia (ATL) has a range of clinical characteristics. Phenotypically the leukemic cells usually express the helper/inducer associated antigen OKT4 with lack of OKT8. We have observed three patients with acute ATL cytologically indistinguishable from OKT4+/OKT8- ATL but whose neoplastic cells had the unusual phenotype, OKT3+, OKT4+, OKT6-, OKT8+ OKT9+/-, OKT11+, Tac+/-, TdT-. All patients had abnormal karyotypes and antibodies against anti-ATL associated antigens as well as proviral DNA of human T-cell leukemia virus in the leukemic cells. The clinical course was complicated by skin eruptions, hypercalcemia, pulmonary infection and disseminated intravascular coagulopathy. All died of complications shortly after diagnosis. The clinical features of these patients were similar to those of OKT4+/OKT8- ATL. However, their acute course suggests that co-expression surface antigens OKT4 and OKT8 may be a sign of aggressive nature of the disease with poor prognosis.