Aim The present study was a comparison of the validity of the Medication Adherence Self‐Report Inventory (MASRI) questionnaire with other methods of assessing adherence to antimuscarinic drugs treatment in older patients with urge incontinence. Methods The experiment involved 733 men and women aged >65 years who had noted no less than one urge incontinence episode per day. At the beginning of the experiment, and after 4, 8 and 12 weeks, their adherence to treatment was monitored using the MASRI. Results The construct validity of the tool was confirmed by data on the correlation of the percentage of non‐adherent patients according to the MASRI and the percentage of patients having a belief barrier on the Brief Medication Questionnaire screen (r = 0.89, P ≤ 0.01; r = 0.91, P ≤ 0.01; and r = 0.91, P ≤ 0.05 at the 4th, 8th and 12th week of the follow up). The hypothesis of competitive validity was supported by comparing the percentage of non‐adherent patients according to the MASRI and the number of missed doses on the Brief Medication Questionnaire screen (r = 0.94, P ≤ 0.01; r = 0.85, P ≤ 0.05; and r = 0.7, P ≤ 0.05), and according to a visual count of pills. The area under the curve at the 4th, 8th, and 12th week was 0.95 ± 0.04, 0.92 ± 0.03 and 0.94 ± 0.04, respectively. Conclusion The MASRI questionnaire has high validity, and is effective for evaluating adherence to treatment among older patients with urge incontinence taking antimuscarinic drugs. Using the MASRI would imply lower costs and greater availability of diagnostics, and it is the tool of choice in clinical practice. Geriatr Gerontol Int 2017; ••: ••–••.