We analyzed the prevalence, inheritance, progression, and functional implications of spinal deformity in Marfan syndrome using four different groups of patients. We studied 113 patients who had Marfan syndrome, eighty-two of whom were skeletally immature, in order to characterize the alignment and function of the spine. The patients were selected from a clinic that provides total care with no bias toward the presence of orthopaedic conditions. Scoliosis was identified in fifty-two of the eighty-two patients, and the prevalences for the sexes were equal. The thoracic portion of the curve was convex to the right in all but two patients. The mean kyphosis was greater than that in the general population. Five distinct sagittal profiles were identified on the basis of whether the thoracic kyphosis was within, greater than, or less than normal limits and whether the transition between the kyphosis and lordosis occurred at or caudad to the normal level or whether the curves were reversed. Spondylolisthesis was present in five patients (6 per cent), with a mean slip of 30 per cent. Fourteen pedigrees were studied in depth. There was no familial pattern of the scoliosis. A separate group of fifty-six patients with scoliosis, for whom serial follow-up radiographs were available, was studied for progression. Patients who had a curve of more than 30 degrees had mild progression, and those who had a curve of more than 50 degrees had marked progression (mean, 3 +/- 4 degrees per year). Pain and function of the back were studied in thirty patients who were thirty-five to forty-five years old; these patients were found to be more impaired than matched controls. The presence of scoliosis was associated with pain in the region of the curve in these patients.