Determine the clinimetric properties of the de Morton Mobility Index (DEMMI) in an adult inpatient rehabilitation population.Prospective open cohort case series. DEMMI and functional independence measure assessed within three days of admission and discharge and seven-point Likert assessment of global change in mobility during inpatient rehabilitation reported by the patient, physical therapist and rehabilitation physician.A total of 366 patients had assessments of the DEMMI completed on both admission into and discharge from rehabilitation. There was no floor or ceiling effect observed in the sample, but there was a mild (19%) ceiling effect at discharge in patients with a stroke. Evidence was obtained for the convergent, discriminant and known group validity of the DEMMI. The minimal clinically important difference was obtained using two methods. The DEMMI was highly responsive to change (Cohen's d = 1.3).The findings give support to the use of the DEMMI in rehabilitation patients and on the basis of previous studies, support the use of the DEMMI across the continuum of hospital settings. Implications for rehabilitation This study provides evidence that the clinimetric properties of the de Morton Mobility Index (DEMMI) are sound. The findings give support to the use of the DEMMI in rehabilitation patients. Our findings, in conjunction with previous research, support the use of the DEMMI across the continuum of hospital settings.