Glucocorticoid-induced myopathy is a characteristic symptom of endogenous Cushing's syndrome. Its long-term outcome is largely unknown.To evaluate long-term muscle function following remission of endogenous Cushing's syndrome.Observational longitudinal cohort study.Tertiary care hospitals and specialized outpatient clinic.As part of the prospective multicenter German Cushing's Registry we assessed muscle strength in patients with overt endogenous Cushing's syndrome. We studied the patients at the time of diagnosis (n=88), after 6 months (n=69) and thereafter annually following surgical remission over a period of up to four years (1 year: n=55; 2 years: n=34; 3 years: n=29; 4 years: n=22). Muscle function was evaluated by hand grip strength and by chair rising test.Grip strength was decreased to 83 % of normal controls (100 %) at time of diagnosis. It further decreased to 71 % after 6 months in remission (p≤0.001) and showed no improvement during further follow-up compared to baseline. Chair rising test performance improved initially (8 seconds at baseline vs 7 seconds after 6 months, p=0.004) but remained at this reduced level thereafter (7 seconds after 3 years vs 5 seconds in controls, p=0.038). In multivariate analysis we identified as predictors for long-term muscle dysfunction age, waist-to-hip-ratio and HbA1c at baseline. Furthermore, muscle strength during follow-up was strongly correlated with quality of life.This study shows that Cushing's syndrome associated myopathy does not spontaneously resolve during remission. This calls for action to identify effective interventions to improve muscle dysfunction in this setting.