DNA flow cytometry (FCM) was performed on paraffin-embedded tissue blocks of 38 surgically resected colorectal carcinomas (CRC). Forty-seven percent of tumors exhibited aneuploidy and 53% were diploid. Seventy-two percent of patients in the aneuploid but only 35% in the diploid group were alive after a mean follow-up of 30.7 and 28.8 months (p = 0.01), and 5-yr survival of 56.7% and 11.7%, respectively (p less than 0.05). The site of tumor location, Dukes' stage, and serum CEA level did not predict a certain DNA stemline. However, irrespective of the ploidy pattern, a serum CEA level greater than 5.0 was associated with a higher mortality and poor 5-yr survival (p less than 0.005). Similarly, advanced Dukes' stage was associated with higher mortality (p less than 0.05). Forty-six percent of the patients with lesions that were Dukes' B2 or advanced stage received adjuvant therapy. Eighty-five percent of this subgroup of patients died; 18% of these patients had aneuploid tumors. The role of FCM in the assessment of prognosis of CRC deserves further clinical evaluation in a randomized control trial.