PURPOSE: To assess the validity of a patient-reported adverse drug events (ADEs) questionnaire with a 3-month or 4-week recall period. METHODS: Patients receiving at least one oral glucose-lowering drug were asked to report potential ADEs they experienced related to any drug in a daily diary for a 3-month period. Thereafter, they completed the ADE questionnaire with either a 3-month or 4-week recall period. The validity was assessed by comparing ADEs reported in each version with those reported in the diary at class level and at specific ADE level. At class level, a comparison was made using (1) primary system organ classes (SOCs) of the medical dictionary for regulatory activities and (2) other related SOCs. Sensitivity and positive predictive value (PPV) were calculated. RESULTS: Each version of the questionnaire was completed by 39 patients. In the 3-month group, 21 patients reported 70 ADEs in the diary. In the 4-week group, six patients reported seven ADEs in the last 4 weeks of the diary. Sensitivity to assess ADEs at primary SOC was low for both recall groups (33 %). PPV was 51 and 10 % for, respectively, the 3-month and 4-week group. Taking other related SOCs into account slightly increased the sensitivity for the 3-month group (38%). Sensitivity of reporting the same ADE was 41 and 43 % for, respectively, the 3-month and 4-week group. CONCLUSIONS: Regardless of the recall period and level of comparison, the validity for assessing ADEs was low with the patient-reported ADE questionnaire. Further refinement is needed to improve the validity.