The DNA histograms of resected rectal carcinomas from 121 patients were compared, along with a detailed clinicopathologic assessment of the same tumors, with the incidence of postresection tumor recurrence and patient survival over an extended period of 15-year follow-up. A poorer prognosis was found for patients with DNA aneuploid and DNA tetraploid rectal cancers as compared with patients with DNA diploid cancers. In addition, local tumor recurrence was twice as common among patients with DNA nondiploid rectal carcinomas. The DNA pattern of a rectal carcinoma was an independent prognostic variable in a Cox's multivariate analysis model. DNA nondiploid rectal carcinomas had a statistically significant increased incidence of vascular invasion, tumor fibrosis, and high Dukes' stage.