Aim: To investigate the relationships among the Gross Motor Function Classification System (GMFCS), Manual Ability Classification System (MACS), and Communication Function Classification System (CFCS) in children with cerebral palsy (CP). Method: Using questionnaires describing each scale, mothers reported GMFCS, MACS, and CFCS levels in 222 children with CP aged from 2 to 17 years (94 females, 128 males; mean age 8y, SD 4). Children were referred from pediatric developmental/behavioral, psychiatry, and child neurology clinics, in the USA, for a case-control study of the etiology of CP. Pairwise relationships among the three systems were assessed using Spearman's correlation coefficients (r[subscript s]), stratifying by age and CP topographical classifications. Results: Correlations among the three functional assessments were strong or moderate. GMFCS levels were highly correlated with MACS levels (r[subscript s] = 0.69) and somewhat less so with CFCS levels (r[subscript s] = 0.47). MACS and CFCS were also moderately correlated (r[subscript s] = 0.54). However, many combinations of functionality were found. Of the 125 possible combinations of the three five-point systems, 62 were found in these data. Interpretation: Use of all three classification systems provides a more comprehensive picture of the child's function in daily life than use of any one alone. This resulting functional profile can inform both clinical and research purposes.