The incidence of clinically significant prostate disease in Asian men is lower than in Western men and appears to be influenced by dietary and environmental factors. The aim of this study was to examine the effect of dietary isoflavones on prostate growth in intact male mice using an extract of red clover. The results demonstrated that prostate, but not testis, size was significantly reduced over 28 days of a red clover isoflavone supplemented diet. Histological examination revealed an increase in apoptotic cells, rather than a reduction in proliferative activity in the epithelium. These findings support the hypothesis that dietary red clover isoflavones can induce apoptosis and lead to a reduction in prostate size.