BACKGROUND AND AIM: Age, ethnicity and family history are the only established risk factors for prostate cancer, but they are not modifiable. Other risk factors have been investigated, with inconsistent findings. A possible role of air pollution, which has been classified as a human carcinogen, has been suggested yet there have been few studies of prostate cancer. METHODS: We conducted a case-control study in eight Canadian provinces to investigate the relationship between PM2.5 and NO2 and incident prostate cancer. Participants provided data between 1994 and 1997 and the development of air pollution historical surfaces now permits risks to be estimated. 1416 cases of prostate cancer and 1426 controls who reported addresses between 1975 and 1994 were examined. Three methods were used to measure the mean exposure to PM2.5 and NO2: (1) satellite-derived observations; (2) satellite-derived observations scaled with historical fixed-site measurements of PM2.5 and NO2; and (3) a national land-use regression (LUR) model for NO2. Odds ratios (OR) and 95% confidence intervals (CI) were estimated per interquartile range (IQR) increase in PM2.5 and NO2 using logistic regression. RESULTS:We found a positive association between prostate cancer and both measures of PM2.5 from 1975 to 1994; for an increase of 1 IQR of PM2.5, the OR adjusted for personal and contextual factors was 1.27 (95% CI: 1.09-1.54) while for the satellite derived-observation the OR was 1.21 (95% CI: 1.04-1.41). We also observed positive associations for NO2. The ORs for satellite-derived observations and scaled satellite-derived observations of NO2, adjusted for personal and contextual factors, were 1.05 (95% CI: 0.93-1.19) and 1.15 (95% CI: 0.97-1.36) per IQR increase, respectively. CONCLUSIONS:Our study highlights a potential role of air pollution in prostate cancer etiology. Given the paucity of studies on this topic, further research is needed exploring the role of screening and variations in risk by prostate cancer aggressiveness. KEYWORDS: prostate cancer, air pollution, PM2.5, NO2, case control study, Canada