The aim of this study was to examine the ability of the Functional Mobility Scale (FMS) to detect change in children with cerebral palsy (CP) undergoing single event multilevel surgery (SEMLS). A retrospective study was conducted of gait laboratory records and video assessments for a consecutive sample of children with CP aged 4 to 18 years who were managed by multilevel surgery. FMS ratings and Gross Motor Function Classification System (GMFCS) levels were recorded preoperatively and at regular postoperative time points. The sample comprised 66 children (32 females, 34 males) with spastic diplegia, GMFCS Levels I (n=18), II (n=24), and III (n=24). The mean age at surgery was 10 years (SD 2y 6mo, range 6-16y). For each FMS distance (5, 50, and 500m) odds ratios showed significant deterioration in mobility at 3 and 6 months postoperatively. Mobility then improved to baseline levels by 12 months and improved further by 24 months postoperatively. GMFCS level remained stable throughout most of the postoperative period for children classified as GMFCS Level III preoperatively but not for children classified as Levels I or II. The FMS was found to be a clinically feasible tool for quantifying change after SEMLS in children with CP.This investigation examines the ability of the Functional Mobility Scale (FMS) to detect change following single event multilevel surgery (SEMLS) in children with cerebral palsy (CP). The FMS is an evaluative measure of functional mobility in children with CP aged 4 to 18 years. Although the FMS is used in clinical practice and initial testing has been conducted, 1 further validation is required because not all aspects of validity were adequately explored in the previous study.For children with CP, the correction of musculoskeletal deformities producing gait deviations is usually performed in one session. 2 SEMLS refers to the correction of all orthopaedic deformities in one session 3 and can be defined as at least two orthopaedic procedures at different anatomical sites in each limb (i.e. a minimum of four procedures). 4 To determine the effects of major interventions such as SEMLS, there is a need for tools that can accurately measure change over time in activities such as mobility. The FMS quantifies functional mobility, which is a key aspect of the activity and participation domains of the International Classification of Functioning, Disability and Health. 5 Using this classification, activity is conceptualized as 'the execution of a task or action by an individual' and participation is 'the involvement in life situations'. Functional mobility enables children with CP to move around within the home, school, and community environments to allow participation in the family setting and society.A unique feature of the FMS is the ability to distinguish between different assistive devices used by the children at home, school, and in the wider community. Assistive devices range from walkers and crutches to wheelchairs. The FMS measures performance, which is what the child 'does do' in the usual ...