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 5to 33 years). Their scoliotic deformities were treated with custom-moulded, polypropylenethoraco-lumbar-sacral orthoses. Cobb angles were measured on radiographs taken in a sitting positionbefore 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-twopatients 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.