Background: Obesity and diabetes are established risk factors for colorectal cancer but have mainly been assessed independently. There are few data about whether the metabolic syndrome, which refers to a clustering of cardiovascular disease risk factors thought to be related to insulin resistance, including obesity, type 2 diabetes, hyperlipidemia, and hypertension, is associated with colorectal cancer risk. Methods: During and after the randomized trial of aspirin and B-carotene, 22,071 healthy male physicians, initially ages 40 to 84 years, reported overweight (body mass index, z27 kg/m