Proxies typically serve as information providers in studies of persons with intellectual disabilities. However, little is known about the concordance between different proxy categories and how proxy characteristics influence the information provided. We compared 89 pairs of relative and staff reports on the living conditions of persons with intellectual disabilities, using percentage agreement and Cohen's kappa statistics. Results demonstrate differences between relative and staff reports for most of the domains investigated, with moderate agreement for objective items and fair agreement for subjective items. Relative and staff proxies contributed different information related to diverse viewpoints and varying types of information. Thus, we suggest that information provided by proxies should not be treated as being interchangeable but, rather, as complementary.