Introduction: Despite a trend toward the use of perforator-based flaps for autologous breast reconstruction, the m. latissimus dorsi (LD) flap remains a popular alternative. Several studies have sought to uncover the shoulder-related donor-site morbidity, but the results are inconclusive. This study aims at evaluating what impact breast reconstruction with an LD flap has on shoulder strength, range of motion (ROM), lymphedema, sensory disturbances, and patients’ ability to perform activities of daily living (ADL). Materials and methods: In a prospective observational study, we examined 20 female patients undergoing delayed breast reconstruction with an LD flap. The primary outcome was a change in shoulder strength, measured with the Biodex System4 Pro-dynamometer. ROM was assessed using two-dimensional photogrammetry. Furthermore, the patients’ self-reported pain, lymphedema, sensory disturbances, and ability to perform ADL were assessed using a questionnaire. Measurements were performed pre-operatively at 3 months and 12 months post-operatively. Results: Of the 20 included patients, 17 completed the follow-up. At the 12 months follow-up, a significant loss of isometric shoulder strength of 17% was observed in shoulder adduction (P<0.001) and 21% in extension (P<0.001). Isometric strength and ability to perform ADL and ROM were unchanged. There was a decrease in the number of patients reporting problems with lymphedema (10 to 7) and an increase in the incidence of sensory disturbances (10 to 13). Conclusion: A loss of shoulder strength was observed following the transfer of the LD flap; however, the procedure did not hinder the post-operative performance of ADLs for the patients. LD reconstruction seems to be a safe procedure.