Aim: The aim of this study was to describe the course of motor performance and analyse its relationship with motor capacity over a period of 3 years in 104 children (66 males, 38 females; 43% of those initially invited) with cerebral palsy (CP) aged 9, 11, and 13 years at the start of the study. Forty-one had hemiplegia, 42 diplegia, 21 tetraplegia; 83 spastic CP, 17 dyskinetic/mixed, and four ataxic CP. Gross Motor Function Classification System (GMFCS) levels were I, n=49; II, n=15; III, n=10; IV, n=12; and V, n=18. Method: Motor performance (what a child does do) was determined using the gross motor skills subscale of the Vineland Adaptive Behavior Scales and motor capacity [what a child can do] was determined using the Gross Motor Function Measure-66 (GMFM-66). The measurements were performed annually over a period of 3 years. Results: The course of motor performance in mildly affected children (GMFCS level I) was more favorable than in more severely affected children. An increase in motor capacity was significantly related to an improvement in motor performance over the 3 years. Interpretation: Training motor capacity in children with CP seems to be important for improving motor performance. Interventions should also focus on environmental adaptations and improving mobility equipment. A limitation of this study was that the instruments used did not contain the same items on capacity and performance level.