AIM The aim of this study was to examine the relationship between gross motor capacity and daily-life mobility in children with cerebral palsy (CP) and to explore the moderation of this relationship by the severity of CP.METHOD Cross-sectional analysis in a cohort study with a clinic-based sample of children with CP (n=116; 76 males, 40 females; mean age 6y 3mo, SD 12mo, range 4y 8mo-7y 7mo) was performed. Gross motor capacity was assessed by the Gross Motor Function Measure (GMFM-66). Daily-life mobility was assessed using the Pediatric Evaluation of Disability Inventory (PEDI): Functional Skills Scale (FSS mobility) and Caregiver Assistance Scale (CAS mobility). Severity of CP was classified by the Gross Motor Function Classification System (48% level I, 17% level II, 15% level III, 8% level IV, 12% level V), type of motor impairment (85% spastic, 12% dyskinetic, 3% ataxic), and limb distribution (36% unilateral, 49% bilateral spastic).RESULTS Scores on the GMFM-66 explained 90% and 84% respectively, of the variance of scores on PEDI-FSS mobility and PEDI-CAS mobility. Limb distribution moderated the relationship between scores on the GMFM-66 and the PEDI-FSS mobility, revealing a weaker relationship in children with unilateral spastic CP (24% explained variance) than in children with bilateral spastic CP (91% explained variance).INTERPRETATION In children aged 4 to 7 years with unilateral spastic CP, dissociation between gross motor capacity and daily-life mobility can be observed, just as in typically developing peers.Gross motor capacity is the ability to use large groups of muscles to keep one's balance and change positions (e.g. sitting, standing, walking, running, and jumping). In typically developing children, this ability is well established by the age of 5 years. 1 In children with cerebral palsy (CP), which is the most common motor disorder in childhood (with a prevalence of 2 per 1000 live births), 2 this ability is not fully established, 3 even in children over 5 years of age with the best functional characteristics. 4 In general, gross motor capacity can be considered an important basis for movement activities of daily living or daily-life mobility. In typical development, children's daily-life mobility gradually dissociates from their gross motor capacity as it becomes increasingly determined by other intrinsic (cognitive and personal) and extrinsic (contextual) factors. 1 Both the concept of gross motor capacity and the concept of daily-life mobility are found within the activities domain of the International Classification of Functioning, Disability and Health. 5 Although the two concepts can be distinguished by qualifying them, respectively, as 'capacity' and 'performance', various qualifiers are frequently used interchangeably, causing confusion even within the domain of activities. In the field of motor control, the ambiguity of qualifiers such as 'ability', 'capacity', 'capability', 'skill', and 'performance' has been criticized. 6 In unravelling the complex relationships in the development...