Causes of long term disability (LTD) were collected between January 1, 1981 and December 31, 1990 among all active pilots in a cohort of Air Canada pilots. During this 10-yr period, 474 (20.9%) of the 2271 pilots had LTD; there were 1107 cases of LTD corresponding to a total duration of leave of absence of 4161 mo. Frequencies of the main diagnostic categories were: injuries: 249 (22.5%); mental disorders: 175 (15.8%); circulatory system: 157 (14.2%); digestive system: 128 (11.6%); and musculoskeletal system: 121 (10.9%). LTD rates increased with age, ranging from 1.86-9.22 per 1000 pilots per year from the younger (20-29 yr) to the older age group (50-59 yr), respectively. Several causes of LTD could be potentially preventable, in particular injuries which accounted for 63.6% of all causes in the younger age group and remained a significant condition at subsequent ages.