A review of 308 cases of colorectal carcinoma showed 12 cases (3.9%) of colorectal multiple primary malignant tumors and 14 cases (4.5%) of colorectal primary malignant tumor associated with extracolonic primary malignant tumor. A total of 60 tumors was involved: 14 each in the sigmoid and transverse colon; eight in the cecum; six in the rectum; one each in the ascending and descending colons; three each in the bladder and prostate; two each in the breast, cervix, and lung; and one each in the skin, nasopharynx, kidney, and endometrium. Three of the four patients with multifocal cancer were found to have in situ cancer, and 12.7% of concomitant adenomas had malignant changes. Seven patients had regional lymph node metastases. Of the six patients with rectocolonic multiple tumors who had adequate follow-up data, survival in three ranged from 19.5 to 60 months; three were alive and well 15 to 51 months after resection. Survival of patients with primary rectocolonic and extracolonic tumors was similar. From these data and the pathologic study of the resected specimens, we recommend for any patient with cancer of the rectocolon that the entire colon be searched for multiple primary malignant tumors, that extracolonic tumors be considered second primary tumors unless proved to be metastases, and that follow-up be long and include frequent rectocolonic examinations for a second primary tumor.