A case has been presented in which thrombocytopenic purpura was a complication of infectious mononucleosis. A review of the literature revealed 6 other cases in which there was an association between these conditions. Serial platelet counts were made in 7 consecutive cases of infectious mononucleosis. There was a slight depression of the platelets early in the illness, followed by a thrombocytosis and a subsequent return to normal. Hypersplenism is considered as a possible cause for the thrombocytopenia in infectious mononucleosis.