This study estimated medical expenditures attributable to cerebral palsy (CP) among children enrolled in Medicaid, stratified by the presence of co-occurring intellectual disability (ID), relative to children without CP or ID. The MarketScan[R] Medicaid Multi-State database was used to identify children with CP for 2003-2005 by using the "International Classification of Diseases, Ninth Revision; Clinical Modification" (ICD-9-CM) code 343.xx. Children with ID were identified for 2005 by using ICD-9-CM code 317.xx-319.xx. Children without CP or ID during the same period served as control subjects. Medical expenditures were estimated for case and control children for 2005. The difference between the average expenditures for children with and without CP was used as a proxy for attributable expenditures for the condition. The attributable expenditures of co-occurring ID were calculated similarly as the difference in average expenditures among children with CP with and without ID. A total of 9927 children with CP were identified. Among them, 2022 (20.3%) children had co-occurring ID recorded in medical claims. Children with CP but without ID incurred medical expenditures that were $15,047 higher than those of control children without CP or ID. By contrast, children with CP and co-occurring ID incurred costs that were $41,664 higher, compared with control children, and $26,617 more than children with CP but without ID. Administrative data from a large, multistate database demonstrated high medical expenditures for publicly insured children with CP. Expenditures approximately tripled for children with CP and co-occurring ID. (Contains 1 figure and 5 tables.)