The UK incidence of prostate cancer has been increasing in men aged < 60 years. Migrant studies and global and secular variation in incidence suggest that modifiable factors, including a high-fat diet, may contribute to prostate cancer risk. The aim of the present study was to investigate the role of dietary fat intake and its derivatives on early-onset prostate cancer risk. During 1999-2004, a population-based case-control study with 512 cases and 838 controls was conducted. Cases were diagnosed with prostate cancer when < or = 60 years. Controls were sourced from UK GP practice registers. A self-administered FFQ collected data on typical past diet. A nutritional database was used to calculate daily fat intake. A positive, statistically significant risk estimate for the highest v. lowest quintile of intake of total fat, SFA, MUFA and PUFA was observed when adjusted for confounding variables: OR 2.53 (95 % CI 1.72, 3.74), OR 2.49 (95 % CI 1.69, 3.66), OR 2.69 (95 % CI 1.82, 3.96) and OR 2.34 (95 % CI 1.59, 3.46), respectively, with all P for trend < 0.001. In conclusion, there was a positive statistically significant association between prostate cancer risk and energy-adjusted intake of total fat and fat subtypes. These results potentially identify a modifiable risk factor for early-onset prostate cancer.