1. Two cases of infectious mononucleosis complicated by acute hemolytic anemia are presented. One of these patients had, in addition, an underlying Mediterranean anemia.
2. Hemolytic anemia is a rare complication of infectious mononucleosis.
3. Thirteen similar cases have been collected from the literature, and the cumulative data summarized.
4. Recovery occurred in all cases. Splenectomy was considered necessary in only two.
5. The etiology of hemolytic anemia in infectious mononucleosis is obscure but there is good evidence to indicate it may be different in different cases. Hypersplenism initiated by infectious mononucleosis could best explain the authors’ cases whereas the elaboration of hemolytic antibodies would best explain some of the reported cases.