Objectives: We conducted a systematic review to identify adverse effects of physical activity and/or exercise for adults with osteoporosis/osteopenia. We synthesised evidence from observational studies, and updated three previously published systematic reviews. Methods: We searched MEDLINE, EMBASE, CINAHL, Web of Science, grey literature and reference lists of relevant studies. Selection criteria were: (1) observational studies in patients with osteoporosis/osteopenia; and (2) in accordance with the criteria used in the previous reviews. A narrative synthesis was conducted for the observational data. Random effects meta-analysis was undertaken for the review updates. Results: For the observational synthesis 14 studies were included. The majority of studies reported no adverse events, reduced incidence/improvement, or no significant change after physical activity or exercise. Activities that involved spinal flexion (certain yoga moves and sit-ups) were associated with a greater risk of vertebral fractures but these events were rare. For the update of reviews, 57 additional studies were identified. Exercise was generally associated with a greater number of minor adverse events including mild muscle/joint pain. Serious adverse events were rare and could not be attributed to the intervention. Conclusion: Patients with osteoporosis/osteopenia can safely participate in structured exercise programmes, whether at home or in supervised facilities. Systematic review registration for observational studies: PROSPERO 2017: CRD42017070551