Epidemiologic investigations have suggested a relationship between dietary fat intake and various types of cancer incidences. Furthermore, epidemiologic studies as well as studies with animal models have demonstrated that not only the amount but also the type of fat consumed is important. At present, the mechanism by which dietary fat modulates carcinogenesis has not been elucidated. The effects of dietary fat on the development of tumours have been summarized in the present review with emphasis on colorectal, pancreas, breast and prostate cancer. It is concluded that influence on synthesis of prostaglandins and leukotrienes may be the universal mechanism by which dietary fats modulate carcinogenesis. Copyright (C) 1999 Elsevier Science B.V.