Prostate cancer is the most common malignant disease in Sweden and the most common cause of cancer-related death among Swedish men. There is, however, a wide geographical variation in the age-standardized incidence and mortality rates. The highest incidence is found in north-western Europe and the US and the lowest in the Asian countries. The reasons for these discrepancies are thought to be related to environmental factors such as variations in dietary pattern. High intake of calories, high Body Mass Index, and consumption of animal fat are all associated with an increased risk of prostate cancer, while high intake of soy and other phytoestrogens, selenium, vitamin A and high serum levels of vitamin D are associated with low risk. As well, gonadal hormones and growth factors are believed to be involved in the complex etiology of prostate cancer. Genetic factors play an important role in the development of prostate cancer, and a hereditary form of the disease, accounting for approximately 5-10% of cases, has been identified. In order to develop effective preventive strategies to reduce prostate cancer mortality and morbidity, it is necessary to expand our knowledge about the etiology of this common disease.