This literature review presents current data on alterations in body composition (BC) in musculoskeletal diseases. Isolated phenotypes – such as obesity, sarcopenia, osteopenia/osteoporosis – and their combinations are considered as possible consequences and modulators of disease pathogenesis. The predominant phenotypes and their prevalence are described: in rheumatoid arthritis the most commonly identified phenotypes are sarcopenia, sarcopenic obesity, isolated obesity, and osteoporosis; in psoriatic arthritis – excess body weight or obesity and sarcopenic obesity prevail; in ankylosing spondylitis – bone mineral density, `osteoporosis, and sarcopenia are most frequent; in osteoarthritis – obesity, sarcopenic obesity, and sarcopenia predominate. The role of proinflammatory mediators and predictors of BC alterations are discussed. The necessity of assessing BC, including in patients with a normal body mass index, is emphasized, and potential approaches to correction of these alterations are also considered.