Among a family of four persons, three members each had a separate malignant disease during a 3-year period. The mother and father concurrently had multiple myeloma and Hodgkin's disease, respectively, and less than 3 years later, their only son was found to have acute granulocytic leukemia. No increased incidence of deaths attributed to Hodgkin's disease, acute leukemia, or multiple myeloma was found in the community. No other cause for this cluster of hematologic malignancies could be found.