Pulmonary function was correlated with patient age and degree of thoracic scoliosis in 25 patients with Duchenne muscular dystrophy in a retrospective, longitudinal study. The observed forced vital capacity (FVC) was found to peak at approximately the age when standing ceases, then to decline rapidly. Thoracolumbar curves were found to be insignificant in adversely affecting pulmonary function in patients with Duchenne muscular dystrophy. Percent FVC was found to be the parameter of pulmonary function that was most strongly correlated with age and scoliosis measurements. In addition, age and thoracic scoliosis together were better predictors of percent FVC than either one alone. Each 1 year of age had approximately the same negative influence on percent FVC that each 10 degrees of thoracic scoliosis had; both decreased percent FVC by approximately 4%. A regression equation for percent FVC is presented which predicts that the patient who has had scoliosis progression halted by spinal fusion would, subsequent to the surgery, show a slower rate of decline of percent FVC and that this rate is quantifiable, predictable, and dependent solely on the patient's advancing age. Therefore, early spinal instrumentation and fusion is advocated in the patient with Duchenne muscular dystrophy.