To evaluate the clinical results of the treatment and to assess the factors that influenced the rate of scoliosis progression, a retrospective study of spinal orthosis in 86 patients with spastic quadriplegic cerebral palsy was performed. The mean age of the patients was 13.8 years (range 5 to 33 years). Their scoliotic deformities were treated with custom-moulded, polypropylene thoraco-lumbar-sacral orthoses. Cobb angles were measured on radiographs taken in a sitting position before treatment, in orthosis, and during follow-up. The mean initial Cobb angle was 68.4° (range 25 to 131°). The mean correction in orthosis was 25° (range 3 to 60°). Seventy-two patients had a follow-up period of more than 2 years. At the latest follow-up, average 6.3 years (range 2 to 14 years) after the start of treatment, the mean Cobb angle without orthosis was 93.1° (range 40 to 145°). The mean progression per year was 4.2° (range –3 to 21°). Linear multiple regression revealed that age and initial correction in orthosis were the only variables that significantly influenced the rate of progression. Twenty-two patients had no progression or progression <1.0° per year. Correction in orthosis was the only variable that predicted progression <1.0° per year in both age groups (<15 years and [ges ]15 years). Of the 57 patients who were still alive and had not undergone surgical fusion, 72% used their orthoses at a mean age of 22 years. Parents and caregivers expressed satisfaction with the use of orthosis, mainly because of improved sitting stability which gave better overall function.