Background Healthcare is a sector with a high risk of musculoskeletal disorders. The work of nurses in a hospital is associated with stress, prolonged work, uncomfortable working postures, bending and twisting of the body and etc. Aim: To identify the risk factors for the frequency and localization of musculoskeletal complaints and diagnosed diseases of the musculoskeletal system in nurses in hospitals. Methods: The study is cross-sectional and comprised 1412 nurses female nurses from 19 hospitals in Sofia having an average age of 50.3±9.9 years. An ergonomic analysis of workplaces in hospitals was made. A survey was conducted in relation to the workplace, the workload, the working posture and movements; Standardized Nordic questionnaires for the analysis of musculoskeletal symptoms were used, BMI. Information on musculoskeletal diseases diagnosed by a doctor was collected with Work ability index (WAI). The statistical analyses were made using SPSS. Results: The frequency of musculoskeletal complaints is high, complaints in the lower back being in the lead with 74.2%, followed by the back, neck and shoulders. A musculoskeletal disorder, diagnosed by a doctor, occurs in 35.6% of the individuals. Widespread is the prolonged work in a standing position, awkward working postures, bending, twisting and stretching. The data from the regression analysis show that the work with bending, twisting and stretching, prolonged work in a standing position and BMI are predictors of musculoskeletal complaints. Conclusion: The results indicate lack of good workplace organisation and equipment. The activity involves prolonged work in a standing position, awkward working postures and work with bending and twisting of the body. High is the incidence of musculoskeletal disorders and the undergone treatment related to them.  Key words: musculoskeletal disorders, workplace, working postures, nurses, hospitals.