Benign prostatic hyperplasia (BPH) and prostate cancer commonly occur together. This suggests that common familial, hormonal, and environmental factors contribute to their development. In men at risk for the development of prostate cancer (at 40 men in 19 families) and aged-matched unrelated controls (n = 46), we have determined whether familial factors, age, and blood hormone concentrations are related to the transition zone (TZ), peripheral zone (PZ), or total volume of the prostate measured by transrectal ultrasound (TRUS). We determined that the influences of age, prostate cancer (n = 15), and familial status did not significantly affect the relationships reported. Therefore, data from all groups were combined for this study. TZ correlated positively with age (P = 0.003) after controlling for family status, but total prostate volume correlated insignificantly with age (P = 0.08). In addition, the ratio of TZ to PZ volumes also correlated significantly with age in the control group (r = 0.27, P = 0.014). Both TZ and PZ volumes correlated highly (r = 0.91, P < 0.0001, n = 86) with total volume. In addition, total volume correlated significantly (r = 0.71, P < 0.001) with the ratio of the TZ/PZ volumes, which also correlated significantly with each other (r = 0.61, P < 0.0001, n = 86). In contrast to the increase of TZ volume related to total prostate volume, PZ volume declined compared with total volume. Prostate volumes up to 50 ml are predominated by the PZ and above 50 ml by the TZ, which may compress and shrink the PZ. Both TZ and total prostate volume correlated positively with serum estrone concentrations (P = 0.04 and P = 0.003, respectively). These results suggest that the risk of prostate cancer does not contribute to generalized overgrowth of the prostate, including the TZ. However, estrogens and age strongly influence TZ but not PZ volume. Both PZ and TZ volumes rise together until the prostate exceeds 50 ml, when the growth of the TZ appears to exceed the PZ and then to compress it.