INTRODUCTION: Back pain is frequently reported by astronauts during the early phase of spaceflight as they adapt to microgravity. The epidemiology of space adaptation back pain has not been well defined. This study aims to develop a case definition of space adaptation back pain, determine its incidence, and assess the effectiveness of available treatments. METHODS: Medical records from the Mercury, Apollo, Apollo-Soyuz Test Project (ASTP), Skylab, Mir, International Space Station (ISS), and Shuttle programs were reviewed. All episodes of in-flight back pain that met the criteria for space adaptation back pain were recorded. Pain characteristics, including intensity, location, and duration of the pain, were noted. The effectiveness of specific treatments was also recorded. RESULTS: The incidence of space adaptation back pain among astronauts was determined to be 52% (382/728). Most of the affected astronauts reported mild pain (86%). Moderate pain was reported by 11% of the affected astronauts and severe pain was reported by 3% of the affected astronauts. The most effective treatments were fetal positioning (91%) and the use of analgesic medications and exercise (primarily treadmill and cycle ergometer), which were both 85% effective. DISCUSSION: This retrospective study examines the epidemiology of space adaptation back pain. Space adaptation back pain is usually mild and self-limited. However, there is a risk of functional impairment and mission impact in cases of moderate or severe pain that do not respond to currently available treatments. Therefore, the development of preventive measures and more effective treatments should be pursued.