Background: Adults with an intellectual disability should be supported according to their individual needs. The perception of need, however, is influenced by the values and expectations of the judging person. Method: Using the Camberwell Assessment of Need for Adults with Developmental and Intellectual Disabilities, self- and proxy-rated needs of n = 193 adults with mild to moderate intellectual disability were compared. Results: Mean total needs and met needs, but not unmet needs, differed significantly between perspectives. As concerns the assessment of specific areas of need, indices revealed a complex and multifaceted pattern of agreement and disagreement. Conclusion: Different viewpoints should be considered when assessing needs among adults with intellectual disability. With respect to areas other than basic, everyday areas of need, involvement of the adult with intellectual disability is strongly recommended. The assessment of mental health problems requires the involvement of clinical professionals, assessing problem behavior broad diagnostic measures beyond a standardized instrument.