In a series of 1,037 patients with colorectal carcinoma diagnosed at one hospital during a 9-year period, synchronous cancers of the colon and rectum occurred in 2 percent. Patient characteristics and presenting symptoms were similar in single and synchronous carcinomas. The frequency of patients with associated benign neoplasms was significantly higher than that in the parent series. An examination of the modified Dukes' classification stage of the lesion in each patient revealed a higher incidence of lymph node involvement and a greater frequency of mucinous adenocarcinoma in patients with synchronous carcinomas. The 5-year survival of patients with synchronous growths did not differ from that of patients with single lesions, even when classified by Dukes' stage. Preoperative diagnosis was difficult, being achieved in no more than 30 percent of patients. Because of the poor accuracy of barium studies, total colonoscopy is the method of choice for this evaluation. We adopted a conservative surgical policy backed by life-long follow-up.