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The purpose of this study was to determine the feasibility and reliability of the modified Berg Balance Scale (mBBS) in persons with severe intellectual and visual disabilities (severe multiple disabilities, SMD) assigned Gross Motor Function Classification System (GMFCS) grades I and II.Thirty-nine participants with SMD and GMFCS grades I and II performed the mBBS twice with 1-week interval. Feasibility was assessed by the percentage of successful measurements per task and of the total score. First, test–retest reliability was determined by intraclass correlation coefficients (ICC) for each task and for the total score of all tasks combined. Second, level of agreement between test–retest scores was assessed with the proportion of equal scores for each task. Finally, internal consistency of the distinct tasks was assessed by Cronbach's alpha.The results indicated that 92% of the measurements by the mBBS for all selected tasks were successful, indicating that the mBBS is a feasible instrument for the tested target group. ICC for the test–retest of the total score was 0.95. The proportion of equal scores for test–retest of the tasks was 0.80 or more, except for tasks 9 and 10. Cronbach's alpha of distinct tasks was 0.84. Test–retest reliability of tasks 9 and 10 was not acceptable.Feasibility of all tasks and test–retest reliability of 10 out of 12 mBBS tasks is acceptable. The mBBS is a both feasible and reliable test for evaluating the functional balance of persons with SMD and GMFCS grades I and II.