Various methods of spinal instrumentation have been used for treatment of unstable fracture & fracture-dislocation of thoraco-lumbar spine. Recently, newly designed short segment fixation devices using pedicle screw were designed and there was a trend to use this posterior short segment instrumentation using pedicle screw. We have used AO internal fixator as posterior instrumentation for unstable spine fracture of thoracolumbar spine since November, 1987. Previously we used Harrington instrumentation and Luque rod wiring for treatment of unstable fracture of thoracolumbar spine and we reported the results of clinical analysis of those systems on Feb, 1987. We analyzed the clinical results of 93 cases those who underwent operative treatment using each posterior instrumentation system for unstable fracture and fracture-dislocation of thoraco-lumabr spine at our hospital from Dec. 1983 to Oct. 1989. Among that 93 cases, the Harrington instrumentation were 35 cases, Luque rod instrumentation were 36 cases and AO internal fixator were 22 cases. The results were as follows:1. The most commonly injured level was Ll (44 case) and followed by T12(33 cases, 86%). 2. By Francis Denis classification, Burst type fracture was most common(42 cases, 45%). 3. Change of kyphotic angle were checked on lateral X-ray view. There no significant differences between those groups using H-rod(58.64%), Luque-rod(54.8%), and AO internal fixator(60.1%) on immediate post-op X-ray. But there noticed least loss of correction of kyphotic angle when using AO internal fixator comparing with other groups. 4. The correction rates of height of anterior and middle column were checked by Denis-Edward method, there noticed best correction rate in AO internal fixator group. 5. The ROM of trunk were checked, there were no significant differences in H-rod, L-rod, and AO internal fixator group in long term follow up.