We conducted a large, sigmoidoscopy-based case-control study to examine the relation of intake of macronutrients, meat, and fiber to occurrence of adenomas of the large bowel. Cases were subjects diagnosed for the first time with one or more histologically confirmed adenomas. Controls had no polyps of any type at sigmoidoscopy, had no history of polyps, and were individually matched to cases by gender, age, date of sigmoidoscopy, and Kaiser Center. The response rate was 84% for cases and 82% for controls. Complete dietary data for 488 matched pairs were available. All odds ratios are from matched analyses adjusted for energy. We observed positive associations with risk of adenomas for calories, animal fat, saturated fat, red meat, and the ratio of red meat to poultry and fish. Protective effects were observed for vegetable protein, carbohydrates, and dietary fiber. The fiber effects diminished after adjusting for fruits and vegetables. Results after mutually adjusting for the effects of saturated fat, fiber and the ratio of red meat to chicken and fish suggest that each of these variables has an effect on risk of adenomas that is independent of the other 2 exposures.