Introduction Mobility is an essential part of a person’s functioning and independence. It encompasses locomotive functions, but also the more basic functions of positioning and transferring. Despite the availability of several mobility-related assessment instruments to date, there is a need for assessment instruments with the specific capability to display the full range of mobilisation. Our aim was to develop and validate a scoring instrument with hierarchical composition where every score value stands for a defined mobility level. Participants and Methods A previously developed and validated pilot instrument was applied to assess patients (n = 113) admitted to an acute rehabilitation programme. Mobility was assessed during admission, subsequently at weekly intervals and at discharge to acquire a detailed status of mobility at multiple time points and individual mobilisation profiles over time. The scoring instrument was then remodelled based on clinical criteria to establish an easy-to-use scoring system with hierarchical composition. Psychometric properties were calculated using an independent sample of 87 consecutive patients. Results Content validity could be affirmed. The psychometric tests demonstrated excellent convergent validity with the three mobility items of the Barthel Index (r = 0.93), despite an adequately lower correlation with the whole Barthel Index (r = 0.63). Adequate floor and ceiling effects (20%) and a large responsiveness to change (ǀdǀ = 1.7, p < 0.001) between admission and discharge values were demonstrated. Inter-rater reliability was excellent (κ = 0.88). Conclusions The Charité Mobility Index (CHARMI) is a promising, easy- to-use hierarchical scoring instrument assessing the full individual spectrum from immobility to unlimited mobility, including positioning, transfer and locomotion items. It allows for monitoring of mobilisation.