Background: Since the DSM-5, adaptive functioning has taken a prominent place in the classification of intellectual disability (ID). The ADAPT was developed to assess adaptive skills in individuals with ID. Method: A total of 2,081 ADAPTs from clients with suspected ID or borderline intellectual functioning and 129 ADAPTs from people from the general population (non-ID) were collected, along with background characteristics. Results: Internal consistency of the ADAPT was high ([alpha] = 0.98). ADAPT scores were positively associated with IQ, educational level and level of independent living. Furthermore, individuals without ID scored significantly higher than the clients on "all" of the 65 ADAPT items. Reference values were established for different IQ groups and living situations. Conclusion: Results suggest that the ADAPT is a valid instrument for measuring adaptive skills in individuals with ID. The reference values may be used for the purpose of estimating the level of ID and the needed intensity of support.