The current study determined the test-retest reliability and concurrent validity of the Adapted Short QUestionnaire to ASsess Health-enhancing physical activity (Adapted-SQUASH) in adults with disabilities. Before filling in the Adapted-SQUASH twice with a recall period of two weeks, participants wore the Actiheart activity monitor up to one week. For the test-retest reliability (N=68), Intraclass correlation coefficients (ICCs) were 0.67 (p<0.001) for the total activity score (min x intensity/week) and 0.76 (p<0.001) for the total minutes of activity (min/week). For the concurrent validity (N=58), the Spearman correlation coefficient was 0.40 (p=0.002) between the total activity score of the first administration of the Adapted-SQUASH and activity energy expenditure from the Actiheart (kcals kg-1 min-1). The ICC was 0.22 (p=0.027) between the total minutes of activity assessed with the first administration of the Adapted-SQUASH and Actiheart. The Adapted-SQUASH is an acceptable measure to assess self-reported physical activity in large populations of adults with disabilities, but is not applicable at the individual level due to wide limits of agreement. Self-reported physical activity assessed with the Adapted-SQUASH does not accurately represent physical activity assessed with the Actiheart in adults with disabilities, as indicated with a systematic bias between both instruments in the Bland-Altman analysis.