Ninety-one patients with idiopathic scoliosis, who underwent posterior spinal fusion and instrumentation from January 1977 to December 1982, were reviewed. All patients were 20 years or older at the time of surgery and none had undergone a prior surgical procedure. Indications for surgery included pain, progressive deformity, and pulmonary symptoms. All patients had a posterior spinal fusion with Harrington instrumentation and autogenous iliac bone graft, with the addition of segmental wiring in only eight. No patient had an anterior fusion or fusion to the sacrum. Follow-up averaged 3.5 years (range: 2-7 years). The average correction at the time of surgery was 38%, and 32% at the time of last follow-up. Seventy-nine percent of the patients reported complete relief of the symptom(s) for which they had surgery. There were 34 complications in 30 (33%) patients. Pseudarthrosis occurred in 14 (15%), requiring 15 additional procedures to achieve a solid arthrodesis. Urinary tract infection occurred in 8 (9%) patients and Harrington hook dislodgement in 5 (5%). One patient sustained a partial paraparesis with recovery to a minimal deficit. No deaths occurred. Although largely successful, posterior fusion with Harrington instrumentation for adult scoliosis has a significant incidence of pseudarthrosis and instrumentation problems.