During the course of the Royal Canadian Air Force Electrocardiographic Program (1939-1986) a selected study of fit aircrew with right bundle branch block was studied. This review covers a period of 18 years during which a consecutive study of 139,651 men from 1960 to 1978 was carried out. Incomplete right bundle branch block of 0.10 s to 0.12 s occurred in 65 cases and complete right bundle branch block in 103 cases. The ages and follow-up periods are discussed. This study, in agreement with recent studies, indicates that right bundle branch block, both incomplete and complete, in itself does not indicate a dire prognosis, particularly when found in young men applying for aircrew training. The final conclusion is that right bundle branch block occurring in young applicants for aircrew training does not preclude their acceptance and this is now (since 1953) the policy of the Canadian armed forces.