1. The prognosis of paralytic scoliosis has been studied by defining curve patterns and establishing the natural development as seen in fully grown patients who have not had surgical correction. 2. The prognosis, unlike that in idiopathic scoliosis, is related to the age of onset of the curvature and the degree of muscle imbalance rather than the site of the primary curve. 3. Paralysis of limb muscles is shown to be unrelated to the development of scoliosis. The intercostal muscles and the lateral abdominal flexors produce scoliosis when weaker on the convex side of the curve. Gravity and the other trunk muscles certainly play a part in the development of lumbar curves but their importance is difficult to assess.