This study was designed to use a prospectively analyzed, population-based, multiethnic cohort of men to determine if there is a relationship between one measure of obesity/overweight (Body Mass Index) and Prostate Specific Antigen (PSA). A total of 1565 men without a prior diagnosis of prostate cancer were prospectively enrolled in the San Antonio study of Biomarkers Of Risk (SABOR) Clinical and Epidemiologic Center of the Early Detection Research Network of the National Cancer Institute. Body Mass Index (BMI) was compared with serum PSA levels, stratifying by ethnic group. No relationship was found between BMI and PSA in any ethnic group or in the cohort as a whole. This study suggests that there is no increased risk of overdetection of prostate cancer among obese men due to an elevation in PSA.