Prostate cancer (PC) is a common and very heterogeneous disease ranging from slow-growing tumours to aggressive tumours with lethal outcome. Obesity and related lifestyle factors have been hypothesised to promote PC progression, but few risk and prognostic factors have been confirmed in PC, and the joint impact by PC heredity – one of few known strong risk factors – is unknown. The aim with the project is to investigate 1) obesity (body mass index and waist circumference), 2) blood lipids (triglycerides, low- and high-density lipoprotein), and 3) smoking, in relation to PC risk by tumour spread and aggressiveness, and, among cases, to PC prognosis. The study is a large-scaled epidemiological study of 420,000 men in Sweden with information from health examinations, linked to nation-wide registries, including the clinical PC registry. We use various methods to strengthen the case for cause and effect, i.e. supporting that the risk factors cause PC and are not just correlated with PC, and we study the associations in interaction with PC heredity. The results are expected to substantially improve the scientific basis for lifestyle advice for the prevention and treatment of PC, in particular targeted at high-risk groups such as men with PC heredity, and lethal PCs.