Although much has been written, little is known about the causes of prostate cancer. Variations between populations in the incidence of invasive cancers, together with changes in the incidence of invasive cancers in migrants, have pointed to environmental (lifestyle) factors that might be amenable to intervention. Conversely, there is a lack of international variation in the prevalence of microscopic tumours, so the essential question is: what causes only some of the common microscopic tumours to become aggressive? Dietary factors hold the most promise in this regard and have been the subject of recent reviews. The strongest and most consistent effects are positive associations with animal products such as red meats, eggs and dairy foods, and possibly by implication, fat. Evidence of a protective effect of fruit and vegetables is weak and inconsistent, as is the relationship with vitamin A and carotenoids, such as beta-carotene. There are some interesting leads. Lycopene, the carotenoid found in tomatoes, has been reported to be protective; alpha-tocopherol supplementation has shown a protective effect in one intervention study; and vitamin D has been shown to be protective in a prospective study. Interest is also growing in phytoestrogens and the extent to which dietary manipulation with these and other phytochemicals might influence prostate cancer by modifying male sex hormone levels or actions. There is limited evidence of associations with obesity. It is not known whether these are related to a particular dietary pattern or to possible physiological effects on the male's hormonal milieu. Associations with lean body mass are likely to be related to the action of androgens during growth and development. Dietary and nutritional effects on prostate cancer do not appear to be strong, but they may be subtle and attenuated by measurement error. To explore these aspects further will require large prospective studies that include improved (repeated) dietary measurements and also blood sampling, so that genetic polymorphisms can be adequately investigated. Such studies are underway.