Background: Staff and relatives often act as advocates for people with severe to profound intellectual disability (ID). Since staff and relatives make proxy judgements about quality of life for people with severe to profound ID, it is important to know how well the perceptions of the two groups correspond with each other. Method: Fifty-one staff-family dyads completed the QOL-PMD questionnaire. Agreement between proxies was assessed using the proportion of observer agreement (Po) and Wilcoxon signed-rank tests. Results: Proxies agreed relatively strongly about the applicability of questionnaire items. There was also relatively strong agreement about the client's QOL, except for items related to internal, subjective experiences (e.g., sexual fulfillment, pain). Conclusion: People with severe to profound ID are not able to report their QOL well. Because the people making proxy judgements about their QOL are not in good agreement on some of the most critical subjective indicators, careful information exchange about these indicators is important for improving the QOL of people with ID.