Acromegaly is an infrequent disease attributable to endogenous excess of GH and IGF-I. Human studies have associated the GH-IGF-I axis with the development of colorectal cancer; however, the question of whether colorectal cancer is a problem in acromegaly is currently unresolved. We performed a cross-sectional study to assess the risk of colonic neoplasia in patients with acromegaly. Colonoscopic screening was performed in 235 patients with acromegaly at five tertiary care hospitals in Italy between January 1, 1996, and December 31, 2001. A repeat colonoscopy was performed in 121 patients after a mean interval of 32.1 months. Colonoscopic findings in patients with acromegaly were compared with those of 233 patients with nonspecific abdominal complaints who were referred for endoscopy during the study period. A total of 65 patients (27.7%) and 36 controls (15.5%) had colonic neoplasia. In 55 patients (23.4%) and 34 control subjects (14.6%), the most important findings were adenomas (odds ratio, 1.7; range, 1.1-2.5), whereas 10 patients (4.3%) and two control subjects (0.9%) had carcinoma (odds ratio, 4.9; range, 1.1-22.4). The risk of colonic neoplasia was higher for younger patients with acromegaly compared with age-matched controls. Patients with acromegaly with or without colonic neoplasia did not differ significantly for IGF-I levels or duration of disease. A neoplastic recurrence was found in 16.5% of patients who underwent follow-up; 90% of them had had a neoplasm removed at the first colonoscopy. Acromegaly carries with it a moderate, but definitive, increase in the risk of colonic neoplasia that occurs at a younger age than in the general population. Patients who are found to harbor a colonic neoplasia are at risk for recurrence.