Prostate cancer (PCa) is the most common malignancy in men. The role of the apparent diffusion coefficient (ADC) of biparametric MRI (biMRI) which is a study without the use of dynamic contrast enhancement (DCE), in detection of PCa is still not comprehensively investigated. Objective. The goal of the study was to assess the role of ADC of biMRI as an imaging marker of clinically significant PCa Materials and methods. The study involved 78 men suspected of having PCa. All patients underwent a comprehensive clinical examination, which included multiparametric MRI of the prostate, a component of which was biMRI. The MRI data was evaluated according to the PI-RADS system version 2.1. Results. The distribution of patients according to the PI-RADS system was as follows: 1 point – 9 (11.54 %) patients, 2 points – 12 (15.38 %) patients, 3 points – 25 (32.05 %) patients, 4 points – 19 (24.36 %) patients and 5 points – 13 (16.67 %) patients. In a subgroup of patients with 5 points, clinically significant PCa was detected in 100 % of cases. In the subgroup of patients with tumors of 4 points clinically significant PCa was diagnosed in 16 of 19 (84.21 %) cases, and in 3 (15.79 %) patients – clinically insignificant tumor. In the subgroup of patients with 3 points, clinically significant PCa was diagnosed in 11 of 25 (44.0 %) cases, in 8 (32.0 %) patients – clinically insignificant tumor and in 6 (24.0 %) patients – benign prostatic hyperplasia. PCa with a score of ≥ 7 on the Gleason scale showed significantly lower mean values of ADC of the diffusion-weighted MRI images compared to tumors with a score of < 7 on the Gleason scale: (0.86 ± 0.07) x 10-3 mm2/s vs (1.08 ± 0.04) x 10-3 mm2/s (р < 0.05). Conclusions. The obtained results testify to the high informativeness of biMRI in the diagnosis of prostate cancer. The use of ADC allowed to differentiate clinically significant and insignificant variants of the tumor, as well as benign changes in prostate tissues and can be considered as a potential imaging marker of PCa. Key words: prostate cancer, diagnosis, biparametric MRI, marker, apparent diffusion coefficient, PI-RADS.