Acute lymphocytic leukemia (ALL) is a heterogeneous group of disorders, clinically, immunologically, and pathologically. ALL of a B cell phenotype (B-ALL) is the least common. We have studied ten adult patients with B-ALL, none of whom had a tumor mass. The median age was 56 years (range, 30 to 90). A history of an altered immune state was noted in four cases: a distant history of Hashimoto's thyroiditis in one, pregnancy in one, and acquired immunodeficiency syndrome in two. Two patients presented with CNS involvement, and in two additional patients CNS leukemia developed during the course of disease. By the French-American-British (FAB) classification system, L3 leukemic morphology was present in nine, whereas L2 was present in one. Circulating leukemic blasts varied from less than 500/dL to greater than 15,000/dL. Eight patients were thrombocytopenic, and eight were anemic at presentation. Immunologic marker studies on leukemic blasts revealed monoclonal kappa light chain marking in nine and monoclonal lambda in one. Following chemotherapy, complete remission was achieved in three patients, two of whom experienced relapse within 9 months. The median survival for the group was 3 months, and only one patient experienced long-term, disease-free survival. We conclude that B-ALL in the adult presents with the classic L3 morphologic picture in the majority and is associated with extremely short survival.