A study of the efficacy of new pharmaceutical composition based on the diindolylmethane (DIM) (Infemin) in patients with diagnosis of prostatic intraepithelial neoplasia (PIN). Sixty-eight patients were randomized to two groups. The first group (n=34) received Infemin for 12 months in a dosage 900 mg/day, the second group received placebo. Efficacy was estimated using the clinical, instrumental and morphologic methods. Twelve months on the therapy led to statistically significant increase in the ratio stroma/ parenchyma from 48.75 to 64.38 (p=0.015) in the Infemin group. Morphologic index in 9 patients of Infemin group was lower after 12 months of therapy (0.48 vs 0.36), in 9 patients of control group it has increased from 0.29 to 0.48, without significance. PSA-level, prostate volume and part of patients with chronic inflammation did not change significantly between the groups. This preliminary data shows the positive influence of the studied medication on the PIN, namely – decrease in severity and spread of neoplastic process in the prostate.