Fifteen patients with adult T-cell leukemia/lymphoma (ATLL) were identified in less than a two-year period in the Crown Heights-Bedford Stuyvesant section of Brooklyn, NY. All patients were black; nine patients originated from the Caribbean islands and six from the southern United States. Two of the patients were father and daughter, the first evidence of familial occurrence in the United States. Their clinical course was similar to that of previously described patients with this disorder. To our knowledge, these 15 patients represent the largest series of ATLL reported in the United States. We recommend that ATLL be seriously considered in the differential diagnosis of patients with non-Hodgkin's lymphoma, mycosis fungoides, lymphatic leukemia, or hypercalcemia.