INTRODUCTION: The medical requirements for commercial pilots are issued by the ICAO and the European aviation safety organization JAA. In Norway, the Aeromedical Section of the Civil Aviation Authority assesses whether pilots are medically fit to fly. This study presents the reasons for medical disqualification among the Norwegian commercial pilot population during a 20-yr period. METHODS: Files on all disqualified commercial pilots were reviewed and subdivided into age groups and diagnostic categories. Different disqualification rates were calculated. RESULTS: From the study population of 48,229 pilot-years, 275 pilots were permanently grounded, which gives a 20-yr average disqualification rate of 5.7 per 1,000 pilot-years. DISCUSSION AND CONCLUSIONS: For cardiovascular diseases the disqualification rate was lower after 1997 than before, which is explained by improved treatment and more lenient requirements. In the diagnostic categories, neurology, musculoskeletal, and psychiatric diseases, the disqualification rate increased after 1997. This fact is probably not attributed to more stringent health requirements, but possibly to the attitudes of the pilots, who have become more critical with respect to their subjective perception of their working environment and psychosocial factors.