The benefits of achieving rigid internal fixation and eliminating the need for postoperative external orthotic support with L-rod spinal instrumentation made it desirable for use in the surgical treatment of neuromuscular scoliosis. From May 1981 to May 1985, 31 severely involved cerebral palsy patients with progressive spinal deformity underwent posterior fusion and L-rod instrumentation. All patients except one were nonambulatory. Surgical indications included prevention of curve progression, correction of pelvic obliquity, and achievement of balanced spinal alignment in order to improve sitting balance and tolerance without external spinal orthotic support. Ten patients (Group I), with an average age of 15.2 years, with double major or flexible paralytic C-curves or scoliosis measuring less than 70 degrees, underwent posterior fusion and L-rod instrumentation only. Twenty-one patients (Group II), with an average age of 22.1 years, with thoracolumbar, lumbar, or rigid paralytic C-curves or scoliosis measuring greater than 70 degrees, underwent initial anterior release, bone grafting, and Zielke instrumentation followed by second-stage L-rod instrumentation. In Group I, scoliosis averaged 57 degrees and postoperatively 27 degrees (53% correction). In Group II, scoliosis averaged 88 degrees and postoperatively 36 degrees (63% correction). Fifteen Group II patients had posterior fusion extend into the sacrum using the Galveston technique. Six Group II patients were not fused into the sacrum. Scoliosis and pelvic obliquity were corrected in both groups. Torso decompensation improved to 2.7 cm in the Galveston group, but increased to 5.6 cm at follow-up in the patients not fused into the sacrum.(ABSTRACT TRUNCATED AT 250 WORDS)