During a prospective screening study for recto-sigmoid adenomatous polyps, the influence of the following risk factors was evaluated: age; gender; body mass index; heredity for colorectal malignancy; diabetes; hypertension; constipation; previous gastric surgery; previous gastric acid inhibition; alcohol and cigarette consumption; serum cholesterol; serum triglycerides; and serum gastrin. Screening fibre-sigmoidoscopy of 665 patients (aged between 50 and 60 years) at a clinical rehabilitation centre for gastrointestinal and metabolic diseases showed that 146 had one or several adenomas. The study population was overweight by a mean of about 15%. Comparison of those with and those without adenoma using univariate analysis, showed that the group with adenomas had higher serum triglyceride values, drank more alcohol on a regular or excessive basis, were more frequent smokers, and had a tendency to raised fasting serum glucose. In a multivariate analysis, age, high serum triglycerides and high alcohol consumption were risk factors for recto-sigmoid adenomas. The risk factor profile identified in this study may help in the selection of individuals for screening sigmoidoscopy from a similar background population. It also identifies target conditions for primary prevention of colorectal neoplasia.