Background: Since 1992, the diagnosis and classification of intellectual disability has been dependent upon three constructs: intelligence, adaptive behaviour and support needs (Luckasson "et al." 1992. Mental Retardation: Definition, Classification and Systems of Support. American Association on Intellectual and Developmental Disability, Washington, DC). While the methods and instruments to measure intelligence and adaptive behaviour are well established and generally accepted, the measurement and classification of support needs is still in its infancy. This article explores the measurement and classification of support needs. Method: A study is presented comparing scores on the "ICF" (WHO, 2001) based "I-CAN v4.2" support needs assessment and planning tool with expert clinical judgment using a proposed classification of support needs. A logical classification algorithm was developed and validated on a separate sample. Results: Good internal consistency (range 0.73-0.91, N = 186) and criterion validity (? = 0.94, n = 49) were found. Conclusions: Further advances in our understanding and measurement of support needs could change the way we assess, describe and classify disability.