Abstract Although the Supports Intensity Scale (SIS) was developed for persons with intellectual and developmental disabilities, we argue for its applicability for people with psychiatric disabilities. Previous empirical evidence for the criterion-related validity of SIS for this population is limited, based on only two studies with participants from the same Mexican state. In a nationwide study we found that SIS explained between 48 and 51% of the variance in the dependent measure, indicating very good validity. The profile of individual support needs showed sensitivity to activities relatively specific to people with psychiatric disabilities, further indicating the validity of the scale. Overall, we find SIS to be valid and appropriate instrument for assessing the support needs of this population.