Purpose: Study of validity of the Medication Adherence Self-Report Inventory (MASRI) for use in clinical practice to treat patients with benign prostatic obstruction (BPO) accompanied with overactive bladder (OAB) symptoms.Methods: During 12 weeks of the randomized study, 452 patients with BPO and OAB symptoms (mean age of 61.3 (12.7)) were studied for adherence to the treatment with Tamsulosin, Solifenacin and Trospium using the MASRI. External monitoring instruments included the Brief Medication Questionnaire (BMQ) and the visual remaining pill count. The state of the prostate gland and the lower urinary tract was monitored using questionnaires I-PSS, OAB Awareness Tool, uroflowmetry and voiding diaries.Result: Correlation between the percentage of men non-adherent to treatment (MASRI) and the percentage of patients having a belief barrier on the screen of the BMQ was r=0.89, p0.05, r=0.92, p0.01, r=0.85, p0.05, a number of missed doses on the Regimen Screen of the BMQ was r=0.79; p0.05; r=0.81; p0.05; r=0.75, p0.05, a number of non-adherent patients according to the BMQ was r=0.83 (p0.05), r=0.88 (p0.05), r=0.79, p0.05, the results of the pill count were r=0.65-0.76; p0.05-0.01. These data confirm high validity of the MASRI.Conclusion: The MASRI is a valid tool for rapid assessment of adherence to treatment of patients with BPO and OAB receiving Tamsulosin and antimuscarinic drugs and may be recommended for use in clinical practice.