Accumulation of a lipid, histochemically a phospholipid, in the histiocytes of the splenic pulp was observed in seven patients with thrombocytopenic purpura. Six had classical idiopathic thrombocytopenic purpura with abundant megakaryocytes in the bone marrow. Splenectomy resulted in clinical and hematologic remissions in four of these six, continued thrombocytopenia in the fifth, and in the continued requirement of corticosteroid to maintain a reasonably normal platelet count in the sixth. The seventh patient, who died shortly after splenectomy, had marked hypoplasia of megakaryocytes. Similar lipid accumulation was not seen in more than 700 other spleens, removed for a variety of reasons, reviewed in this study. Platelet phagocytosis has been suggested as a source of the lipid.