Longer-term results of Orthopaedic Selective Spasticity-Control Surgery (OSSCS) on gross motor function in 25 patients with cerebral palsy were investigated and compared to the natural history of 70 non-surgical patients with brain-related disabilities, who were visiting this center, in GML using longitudinal and stratified analysis. Participants were 9 females and 16 males, who had previously undergone OSSCS at 13.1 years (5.3 to 38.9) on the average. There were 8, 2, 3, 5, and 7 patients from level 1 to 5 in the Gross Motor Function Classification System (GMFCS), respectively. Gross Motor Function Measure (GMFM) and Gross Motor Level (GML) were evaluated at pre-operation, one year after surgical intervention and every year thereafter. The average passage observation period was 6.4 years (3.7 to 8.4). A good one year postoperative outcome was obtained in 25 cases (100%) in GML and 23 (92%) in GMFM. Good maintenance was recognized in 22 cases (88%) in GML and 17 cases (68%) in GMFM as observed by postoperative progress. The gross motor function began to deteriorate from around 20 years of age in the no-operation group and experienced a drop for many cases in their late thirties. Even this ages, all of 8 patients of operative group with this ages maintained good results in GML. From these results, we found that OSSCS is an effective surgical intervention and that its effect was maintained for many cerebral palsy cases for the postoperative middle term.