We investigated metric properties of the Slovenian translation of de Morton Mobility Index in patients with musculoskeletal impairments during rehabilitation. The study included 30 inpatients, aged 22-84 years, with musculoskeletal impairments with or without impairment of peripheral nerves. They were assessed repeatedly with de Morton Mobility Index, Functional Ambulation Classification, Ten-metre Walk Test, Six-minute Walk Test, Berg Balance Scale and the motor subscale of the Functional Independence Measure. Convergent validity of de Morton Mobility Index was confirmed by good to very good correlations with the other measurements. Known-groups validity was demonstrated by significant differences in de Morton Mobility Index scores between patients who were not able to walk and those who were able to walk with or without waking aid, at admission and after 4 weeks. Predictive validity of de Morton Mobility Index for functional independence after 4 weeks of rehabilitation was moderate. Minimal clinically important difference of de Morton Mobility Index was estimated to be five points. De Morton Mobility Index was responsive after 2 and 4 weeks of rehabilitation (Cohen's d 1.15 and 0.95, respectively). No floor or ceiling effects were identified. Internal validity of de Morton Mobility Index was confirmed by Rasch analysis. Hence, de Morton Mobility Index is a valid, unidimensional, and responsive measure of mobility for patients with musculoskeletal impairments at rehabilitation regardless of age. Its use is recommended for adult patients at low and basic functioning level.