BACKGROUND:The intensive care unit mobility scale (IMS) is reliable, valid and responsive. Establishing the minimal important difference (MID) of the IMS is important in order to detect clinically significant changes in mobilization. OBJECTIVE:To calculate the MID of the IMS in intensive care unit patients. METHODS:Prospective multi center observational study. The IMS was collected from admission and discharge physiotherapy assessments. To calculate the MID we used; anchor based methods (global rating of change) and two distribution-based methods (standard error of the mean and effect size). RESULTS:We enrolled 184 adult patients; mean age 62.0 years, surgical, trauma, and medical. Anchor based methods gave a MID of 3 with area under the curve 0.94 (95% CI 0.89-0.97). The two distribution based methods gave a MID between 0.89 and 1.40. CONCLUSION:These data increase our understanding of the clinimetric properties of the IMS, improving its utility for clinical practice and research.