BACKGROUND Understanding the relationship between socioeconomic status (SES) and prostate cancer incidence could identify populations that should be targeted for intervention and prevention programs. We examined this relationship within the major racial/ethnic groups during the period 1972 through 1997, which spans the introduction of prostate-specific antigen (PSA) testing. METHODS We used data from the population-based Los Angeles Cancer Surveillance Program to examine age-adjusted prostate cancer incidence rates in five SES groups over three specific calendar periods by racial/ethnic subpopulation (white, black, Asian, and Hispanic) and by stage of disease at diagnosis. Linear regression analysis was used to test for trends in the age-adjusted incidence rates that were associated with increasing levels of SES. All P values were two-sided. RESULTS For men diagnosed with prostate cancer before 1987, when the test for PSA was not widely available, we found no association between SES and the incidence of prostate cancer in any of four racial/ethnic subpopulations or between SES and the stage of disease at diagnosis. In contrast, among men who were diagnosed with prostate cancer after 1987, SES was statistically significantly and positively associated with prostate cancer incidence in men from all racial/ethnic subpopulations except Asians (P =.01 for white men, P =.001 for black men, P =.02 for Hispanic men, P =.06 for Asian men, and P =.01 for all men combined). Higher SES was statistically significantly associated with cancers of earlier stage (P =.01 for localized cancer and P =.00 for regional cancer) for men who were diagnosed with prostate cancer after 1987. CONCLUSIONS The association between SES and prostate cancer incidence after 1987 may reflect more prevalent PSA screening in populations with higher SES due to their greater access to health care. SES should, therefore, be considered an important factor in interpreting variations and time trends in prostate cancer incidence.