Aim: The objective of this longitudinal study was to describe the course of social functioning and communication in children with cerebral palsy (CP) over a 3-year period, its difference with the normative course, and its relationship with disease characteristics and personal and environmental factors. Method: Participants in this study were 110 children with CP (70 males, 40 females) with a mean age of 11 years and 3 months (SD 1y 8mo). Social functioning and communication were measured with the Vineland Adaptive Behavior Scales. Comparisons were made with normative data; data were analysed with generalized estimating equations. According to the Gross Motor Function Classification System (GMFCS), 50 of the 110 children were categorized as GMFCS level I, 16 as level II, 13 as level III, 13 as level IV, and 18 as level V. Results: The course of social functioning over a 3-year period showed an increase in restrictions in children with CP (p less than 0.001). Restrictions in communication increased more in children with the most severe forms of CP (p less than 0.001). In addition to disease characteristics (GMFCS category, presence of epilepsy, and speech problems), personal factors (externalizing behaviour problems) and environmental factors (having no siblings, low parental level of education, and parental stress) were associated with greater restrictions in social functioning and communication. Interpretation: The results indicate that it is important to focus not only on the medical treatment of children with CP, but also on their behavioural problems and social circumstances, and to support the parents so that social functioning and communication in these children may be improved.