Forty-five patients with idiopathic thoracolumbar or lumbar scoliosis were treated with the Harrington, Dwyer, or Zielke instrumentation and fusion. The Harrington group achieved a 55% correction of the primary curves, while the Dwyer and the Zielke groups achieved 88 and 91%, respectively. Overcorrection of the curves occurred in a total of nine cases in the latter two groups. The Dwyer and Zielke instrumentations enabled better correction of the curves with a shorter fusion. At subsequent follow-up, the 'adding on' phenomenon as a result of the shorter fusion in the Dwyer group was unchanged, while that in the Zielke group became gradually resolved. The Zielke instrumentation appears to be the apparatus of choice for treatment of thoracolumbar and lumbar scoliosis.