Medical employment standards (MES) are used to identify and quantify the effects of pathology on a person's ability to carry out their duties. Any person requiring a change in their MES for longer than 28 days should have their permanent MES altered accordingly. In the Royal Air Force this is undertaken by Medical Boards. A retrospective review was performed of all personnel attending RAF Medical Boards for a change in their PMES between 15/1/12 and 31/10/13. The primary reason for downgrade was recorded using ICD-10 code. There were 1,583 PMES downgrades, approximately 800/year. This is approximately 2% of all regular RAF personnel. Musculoskeletal disease accounted for 58% of all cases (923 cases, 500/year). Other causes included medicine and general surgery (23%), mental health (10%), obstetrics and gynaecology (5%) and other causes (4%). The majority of the musculoskeletal cases were arthropathy (42%) or back pain (31%). Musculoskeletal disease is the most common cause for medical downgrade in the RAF. More data are required to ascertain the precise nature of these cases and the level of the imposed limitations. This will allow targeted use of increasingly limited resources to ensure that our personnel are as fit as possible to execute their duties.