Simulated flight in a hypobaric chamber is a fundamental component in the physiological training of aviators. Although rare, there is always a risk of decompression sickness (DCS) in trainees during hypobaric hypoxia training. In this study we aimed to determine the incidence of altitude-induced DCS and the symptoms manifested in trainees and inside chamber observers (ICOs) during the training sessions. We retrospectively reviewed the records of DCS cases during the period of January 1, 2011, and October 1, 2018. The records of 6,657 trainees and 615 ICOs were evaluated. The gender distribution in 6,657 trainees was 6,578 (98.81%) male and 79 (1.19%) female. The numbers of DCS cases in trainees and ICOs were six (0.09%) and two (0.33%), respectively [(ICOs versus trainees - odds ratio (OR): 3.574; 95% CI 0.720-17.744; (p > 0.05)]. All ICOs were male; no DCS incident was observed among female trainees. Recompression treatments were applied on site, and complete recovery was achieved in all cases. Overall DCS incidence was found to be 0.11% among the 7,193 male subjects, which included trainees and ICOs.