The aim of this study was to determine the interrater reliability and stability over time of the Capacity Profile (CAP). The CAP is a standardized method for classifying additional care needs indicated by current impairments in five domains of body functions: physical health, neuromusculoskeletal and movement-related, sensory, mental, and voice and speech, in children from 3 to 18 years of age. The intensity of care in each domain is defined from 0 (no need for additional care) to 5 (needs help with every activity). The intensity of additional care in each of the five separate domains indicates the CAP for the individual child. We developed the CAP to inform the parents and other caregivers of children with non-progressive, permanent neurodevelopmental disabilities, such as cerebral palsy and myelomeningocele, about the consequences of these conditions. To determine interrater agreement and stability over time, the CAPs of 67 children (39 males, 28 females) with a neurodevelopmental disability (mean age 18y [SD 1.2y]; range 14-22y) were assessed based on a semi-structured interview. In addition, the CAPs of the same individuals at the age of 3 years were determined based on a chart review. Interrater agreement of the CAP at the age of 3 was good to very good (weighted kappa 0.64-0.92). Agreement between the CAP at the age of 18 and the CAP at the age of 3 (providing evidence for stability over time) was also good (weighted kappa 0.68-0.77), except for the domain "physical health functions", about which agreement was relatively poor (0.47). We conclude that the CAP is a reliable instrument for classifying the additional needs of a child with a non-progressive, permanent neurodevelopmental disability. The preliminary evidence for the stability over time of such needs according to the CAP should be validated in a prospective study. (Contains 3 tables and 1 footnote.)