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.