In this study, the relationship between the location of colorectal cancer and synchronous benign adenomas was assessed in 591 patients. Adenomas were found in 29.7% of all patients. Patients with cancer of the cecum, ascending colon, and hepatic flexure had the highest percentage of benign adenomas. Patients with right-sided cancer had adenomas in 47% of resected specimens, which percentage was significantly higher than that in the group of patients with left-sided cancer, who had adenomas in 22% of their specimens (p less than 0.001). Patients with cancer and synchronous adenomas were also older (70.2 vs 67.8, p less than 0.02) and more likely to be male (p less than 0.002) than patients with cancer and no adenomas. It is suggested that efforts be made to identify adenomas preoperatively in patients with colorectal cancer. In addition, since patients with cancer and associated adenomas are at increased risk of developing metachronous cancer, the group with right-sided cancer should be part of a particularly active surveillance program.