The records of 54 consecutive patients with Wilson's disease seen at the Mayo Clinic from 1952 through early 1977 were reviewed to determine the frequency fo hematologic abnormalaties in their evaluation. Leukopenia and thrombocytopenia sometimes have been ascribed to treatment with D-penicillamine and its toxicity; however, we have found cytopenia to be a frequent finding in the presenting laboratory data of patients with Wilson's disease. Twenty-eight patients (52%) had thrombocytopenia and 16 of these patients (30% of the total) also had leukopenia. Severe, acute, intermittent hemolytic episodes were the initial and only presenting complaint of one patient. Six of the patients with significant cytopenias had splenectomy, and in all cases the peripheral blood counts returned to normal values. Long-term treatment with D-penicillamine improved the hepatic and neurologic dysfunction in most patients; however, the cytopenias remained unchanged except in three patients (treated 2, 5, and 10 years).