To determine the minimal clinically important difference (MCID) of the Zurich Chronic Middle Ear Inventory (ZCMEI-21), a questionnaire assessing health-related quality of life (HRQoL) in chronic otitis media (COM).In this longitudinal study, 103 patients completed the ZCMEI-21 before and after surgery for chronic otitis media. An anchor-based method including a global rating of change (GRC) was used to assess the MCID of the ZCMEI-21.A total of 103 patients were included. The mean preoperative and postoperative ZCMEI-21 scores were 28.6 (SD 13.6), and 21.8 (SD 12.8), respectively. The mean change was 6.8 (SD 0.8; p < 0.0001). A significant correlation between the ZCMEI-21 scores and the GRC was found (r =  - 0.5; p < 0.001). Using the anchor-based method, the MCID of the ZCMEI-21 was estimated at 5.3 (SD 12.0).Knowledge of values indicating a clinically relevant change in patient-reported outcome measures is important when interpreting effects of different treatment modalities. This is the first study assessing the MCID of a questionnaire measuring HRQoL in COM, i.e. the ZCMEI-21. We recommend a MCID of 5 in COM patients undergoing surgical treatment. This information substantially increases the usefulness of the ZCMEI-21 as an outcome measure in COM as changes can be assessed with regard to their clinical meaningfulness.