Heterocyclic aromatic amines and polycyclic aromatic hydrocarbons are mutagens that are produced in highly cooked meats. A case-control study of 511 patients with colorectal cancer and 500 matched control subjects examined whether consumption of well-done cooked beef is related to the risk of developing large bowel cancer. Approximately 16% of men and women consumed well-done beef, and 50% ate medium-cooked beef. For both sexes, there was no association between consumption of well-done or medium-cooked beef and colorectal cancer. This paper discusses whether questionnaire data accurately reflect dietary intake of heterocyclic aromatic amines and polycyclic aromatic hydrocarbons.