It has been reported that patients with acromegaly may have an increased risk of developing several types of cancers, such as colorectal, breast and prostate tumors. However, some reports do not support these findings and therefore the prevalence of cancers in patients with acromegaly remains controversial. In this study, we determined the prevalence of benign and malignant neoplasms in patients with acromegaly. A retrospective chart analysis was performed on 140 patients with active acromegaly who had attended our outpatient clinic (M/F 54/86, age 55 ± 25 yr, range 21-86). Colon cancer was found in 10 patients, thyroid cancer in 5, breast cancer in 4 and gastric cancer in 2. When compared with the local population, the standardized incidence ratios (SIRs) for thyroid cancer in patients with acromegaly were 61.74 (95% confidence interval (CI): 0.51-114.63) for females and 272.4 (95% CI: 29.12-876.71) for males. The SIRs for colon cancer in the acromegalic patients were 17.4 (95% CI: 4.74-44.55) for females and 19.0 (95% CI: 5.18-48.64) for male patients in comparison with the local population. Of the benign tumors, multinodular goiter and colonic, gastric and gallbladder polyps were observed in 57% (47/83), 39% (31/80), 21% (8/39), and 15% (10/65) of the patients, respectively. This study suggested that patients with acromegaly have an increased risk of colon cancer and polyps. Moreover, it is speculated that the risk for thyroid cancer is increased in male patients. It is therefore recommended that patients with acromegaly should undergo screening colonoscopy and ultrasonography of the thyroid.