In differential diagnosis of BPH and early stages prostate cancer (PC), PSA-density (PSAD) was evaluated in 63 cases with BPH and 82 cases of PC (stage A: 8, B: 17, C: 17, D: 40). Serum PSA values were determined by MARKIT-F PA, and prostate volume was calculated by transabdominal ultrasonography, in which every glands including peripheral zone was visualized in the transverse and sagittal planes, and predicted prostate volume was calculated by three dimension (a x b x c x 0.52). PSAD was determined by serum PSA divided by prostate volume. PSAD values were 0.106 +/- 0.006 (mean +/- SD) in BPH, 0.538 +/- 0.094 in stage A and B of PC, and 2.973 +/- 0.764 in all PC cases. There was a statistical significance (p < 0.005) between BPH and each other groups of PC by student's t-test. In using 0.208 (mean +/- 2 SD of PSAD in BPH group) as a cut-off value, the detection sensitivity was 84% in stage A and B of PC and the specificity was 97% using BPH groups as a control, therefore the efficacy was 93%. In 18 out of 19 cases with BPH having PSA values more than 3.6 ng/ml (false positive group), PSAD values were less than 0.208. PSAD is suggested to be a useful tool for differential diagnosis of BPH and early stages of PC.