Forty-nine acromegalics and 57 controls matched for age and sex underwent colonoscopy. The control group consisted of patients investigated because of atypical abdominal complaints compatible with irritable bowel syndrome or constipation. The exclusion criteria for both groups included: age over 75 years, previous colonic polyps or cancer, previous colonic surgery, rectal blood loss, anemia, previous abdominal radiation, sigmoidoscopy, colonoscopy or barium enema performed for any indication within 3 years prior to the present study. Colonoscopy was successful in reaching the cecum in 72 and 77% of the controls and acromegalics, respectively (p = NS). Eleven (22%) of 49 acromegalics had biopsy-proven colonic adenomas versus only five (9%) of the control group (p < or = 0.05). Multiple adenomas were found in three of the 11 acromegalics and in none of the controls. In five of these 11 patients and in only one of the controls, at least one adenoma was located in the right colon. In addition, acromegalics tended to have larger adenomas. The group of acromegalics with and without adenomas did not differ significantly in age or duration of active disease. In conclusion, the present study shows that acromegalic patients have an increased risk of developing colonic adenomas.