A 21-year-old man had severe thrombocytopenia resistant to corticosteroid therapy. Viral studies of cytomegalovirus were 1:1,024. Although the cytomegalovirus titer returned toward normal (1:16 titer) during a period of three months, thrombocytopenia persisted and continued to remain refractory to corticosteroid therapy. Initial bone marrow morphology, platelet size, and platelet survival and sequestration were not typical of idiopathic thrombocytopenic purpura, and it is doubtful that splenectomy would have been helpful. However, when restudied six months later, platelet size was greatly increased, platelet survival was severely shortened (half-time, 2 1/4 hours), and intense splenic trapping was evident. Splenectomy was performed and resulted in normalization of the platelet count. Cytomegalovirus-associated thrombocytopenic purpura is an unusual disease that may take an unpredictable clinical course. Careful study of the mechanism of thrombocytopenia appears worthwhile when early recovery does not occur.