Microangiopathic hemolytic anemia and thrombocytopenia secondary to disseminated intravascular coagulation is a well-described complication of widely metastatic carcinoma. The authors report four cases of gastric carcinoma, one case of colon cancer, and one case of adenocarcinoma of unknown primary in which the patient developed a syndrome analogous to thrombotic thrombocytopenic purpura, consisting of microangiopathic hemolytic anemia, thrombocytopenia, and renal failure without definite evidence of disseminated intravascular coagulation. In contrast to previous reports, postmortem examination in three of the cases revealed no recurrence or only microscopic foci of residual tumor. In the remaining three, there was clinical and pathologic evidence of grossly disseminated carcinoma. Also in contrast to previous cases, all patients evidenced azotemia and proteinuria at the onset of the syndrome and ultimately uremia was a contributing cause of death. Coagulation profiles showed prolonged thrombin times and elevated fibrin degradation products in four instances and did not distinguish the patients with grossly metastatic disease from those with no tumor or only microscopic residua. Circulating immune complexes containing carcinoembryonic antigen were found in the patient with metastatic colon carcinoma. The syndrome was clinically identical whether or not grossly metastatic tumor was present, and it should not be attributed to advanced disease without definite clinical or pathologic evidence of a recurrence.