The pelvic MR examinations of 40 men without known prostatic disease were reviewed retrospectively. Axial long TR/long TE images were evaluated with respect to prostatic zonal size and signal intensity. Findings were correlated with each patient's age (17-74 years). The central region of the prostate and the peripheral zone enlarged with age; the central gland increased in size by an average of 175% between the second and eighth decades and the peripheral zone increased by an average of 67%. The anterior fibromuscular stroma decreased with increasing age (from an average anteroposterior thickness of 1.2 cm in the second decade to 0.4 cm in the eighth decade) and also became thinner as a function of increasing gland size. The periprostatic venous plexus became less prominent as a function of increasing age, decreasing from 2.5 to 1.5 mm in average maximal diameter, but this venous caliber was not significantly correlated with gland size. The conspicuity of the peripheral zone with respect to the central gland was improved, both as a function of increasing age and increasing gland size, and conspicuity was greatest on long TR/long TE images because of excellent contrast resolution. We conclude that in older age groups, the zonal anatomy of the prostate is more clearly defined than in young patients, both because of morphologic changes in prostate structure and because of physiologic changes resulting in differing zonal MR signal intensities.