OBJECTIVES: Increased risk for colorectal cancer (CRC) has been associated with type 2 diabetes. Despite several studies linking insulin resistance to increased CRC risk, there are limited data on colorectal adenoma risk in diabetic women. We hypothesized that diabetic women would have increased rates of colorectal adenomas relative to a group of nondiabetic women. METHODS: Colorectal adenoma rates were determined in 100 estrogen-negative women with type 2 diabetes mellitus and compared with 500 nondiabetic, estrogen-negative controls. Adenomas were defined as any adenoma or advanced adenoma (villous or tubulovillous features, size >1 cm or high-grade dysplasia). A multivariate model including age, race, diabetes, hypertension, hypercholesterolemia, body mass index, and nonsteroidal anti-inflammatory drug status was used to determine the independent effects of diabetes on colorectal adenoma incidence. RESULTS: Diabetics as compared with nondiabetics had greater rates of any adenoma (37% vs 24%, p = 0.009) and advanced adenomas (14% vs 6%, p = 0.009). Two hundred forty-five obese subjects compared with 355 nonobese subjects had a higher rate of any adenoma (32% vs 22%, p = 0.001). Obese diabetics compared with nonobese, nondiabetics had greater rates of any adenoma (42% vs 23%, p ≤ 0.001) and advanced adenomas (19% vs 7%, p ≤ 0.001). Multivariate analysis showed that adenomas and advanced adenomas were independently predicted by diabetes (p < 0.05) and adenomas by age. DISCUSSION: Women with type 2 diabetes mellitus had higher rates of colorectal adenomas as compared with lean and nondiabetic women. This finding adds to the evidence that type 2 diabetes is an important factor in the progression of the adenoma-carcinoma sequence.