Family history is known to be a prostate cancer (CaP) risk factor for non-Hispanic Whites (NHWs) and African Americans, but little data are available on the risk for Hispanics (Hs). This population-based case-control study used mailed surveys to assess the effects of ethnicity and family history of CaP on CaP risk in Hs and NHWs. Cases (N = 351) were those identified by the New Mexico Tumor Registry as having been newly diagnosed with CaP from October 1, 1994 to October 31, 1995. Controls (N = 618) were randomly selected and frequency-matched to cases by ethnicity and 5-year age groups. Multivariate analyses were conducted using conditional logistic regression. After controlling for age, education, and income in the models, positive family history increased risk for both Hispanics (H) (OR 2.7, 95% CI 1.5-4.7) and non-Hispanic Whites (NHW) (OR 2.0, 95% CI 1.3-3.1), suggesting that having a family history of CaP is a risk factor for both ethnic groups.