The distribution of different malignant tumors was studied in 40 cancer family syndrome (CFS) families with 315 affected family members and a total of 472 separate tumors or malignant diseases. Only families with three or more first-degree family members with colorectal carcinoma were included and other CFS characteristics were required in at least two cases. Colorectal (63%), endometrial (8%), gastric (6%), biliopancreatic (4%), and uroepithelial carcinomas (2%) were the most frequent, and represent the tumors typical of CFS. Families with endometrial cancer (23, 57%) and those without endometrial cancer (17, 43%) did not differ in frequencies of other extracolonic carcinomas. Families with endometrial cancer has more affected members and especially more affected female members than those without endometrial cancer (means, 9.7 and 4.9 versus 5.5 and 1.6 per family, respectively). The authors conclude, therefore, that the occurrence of one or more types of extracolonic tumors in members of CFS families does not provide a firm basis for subdividing the CFS (or hereditary nonpolyposis colorectal carcinoma syndrome.