BACKGROUND: This research aimed to analyze the body composition (BC) of different military units in the Spanish Armed Forces. METHODS: We studied 179 male aircrew members (86 airplane pilots, 15 helicopter pilots and 78 transport aircrew) using bioimpedance. RESULTS: Airplane pilots (AP) had higher means than transport aircrew (TA) in height (179.56 cm vs . 173.90 cm), total body water (46.72 L vs . 42.96 L), intracellular body water (29.45 L vs . 26.89 L), extracellular body water (17.27 L vs . 16.07 L), proteins (12.72 kg vs . 11.63 kg), minerals (4.50 kg vs . 4.15 kg), soft lean mass (60.21 kg vs . 55.29 kg), fat free mass (63.95 kg vs . 58.74 kg), skeletal muscle mass (36.41 kg vs . 33.07 kg), and lower means in body mass index (24.01 kg vs . 25.49 kg), body fat mass (BFM) (13.53 kg vs . 18.81 kg) and percentage of body fat (PBF) (16.83 kg vs . 23.79 kg). Helicopter pilots also had significantly lower means in BFM (13.21 kg vs . 18.81 kg) and PBF (17.11 kg vs . 18.81 kg) than TA. DISCUSSION: The different types of activity between AP (active coping with G forces) and TA (inactive) during operational flights negatively affects the body composition of TA. These results suggest differences in aircrews training and job tasks. Specific training is needed for each unit: it should be individualized, prevent injuries, and be directed by qualified personnel. Bustamante-Sánchez Á, Clemente-Suárez VJ. Body composition differences in military pilots and aircrew . Aerosp Med Hum Perform. 2020; 91(7):565–570.