OBJECTIVE To assess the effect of ageing and body mass index (BMI) on prostate-specific antigen (PSA) among Chinese men from the results of the 2005 Prostate Awareness Week in Singapore. SUBJECTS AND METHODS In all, 2714 men participated in the programme, consisting of 2431 Chinese, 114 Malays, 117 Indians and 52 'others'. Of these, 2410 Chinese men who had a PSA level of <20 ng/mL and were aged >50 years but <80 years were included in the analysis. Height and weight were used to calculate the BMI. The relationship between age and PSA levels was analysed using linear regression and bivariate correlation, and the associations among different groups of BMI and PSA levels were analysed using analysis of variance and covariance. RESULTS PSA levels were significantly correlated with age (correlation coefficient, r = 0.27, P < 0.001). Analyses showed a significant inverse association between PSA level and BMI; mean PSA levels decreased with increasing BMI for both standards (standard classification; geometric mean, GM, PSA of 1.08, 1.06, 0.96, 0.83 ng/mL for a BMI of <18.5, 18.5-24.9, 25-29.9 and > or =30 kg/m(2), respectively, P trend <0.01; and for Asian classification, GM PSA 1.08, 1.09, 0.96, 0.91 ng/mL for a BMI of <18.5, 18.5-22.9, 23-27.5 and > or =27.5, respectively, P trend <0.001). There were significant differences (P < 0.05) in the age-adjusted GM PSA levels for the groups with BMI <25 (1.05 ng/mL) and BMI > or =25 kg/m(2) (0.97 ng/mL). Similarly, there were significant differences (P < 0.05) in the age-adjusted GM PSA levels in those with a BMI of <30 (1.03 ng/mL) and > or =30 kg/m(2) (0.85 ng/mL). CONCLUSION These data suggest that the BMI in Chinese men in Singapore is significantly associated with PSA levels, especially among the obese men aged 70-79 years.