Microangiopathic hemolytic anemia, thrombocytopenia, and renal insufficiency occurred in a mother an daughter when each was in her third decade. The mother had prominent neurological findings, fever, and expired from renal insufficiency. Her daughter's only major symptom was renal insufficiency. The similarity of the mother's illness to thrombotic thrombocytopenic purpura and of the daughter's to adult hemolytic uremic syndrome suggests that these diseases are variants of a single clinical disorder, while their occurrence in direct descendents strengthens the postulate that in selected instances a genetic predisposition to these disorders may be important.