Transpedicular screw instrumentation offers many advantages like greater stability and trigonometric correction of the deformity of spine in the surgery of lumbar spine instability. Its indication, however, is often limited due to several problems like technical difficulties and instrumental failures. The authors have tried to evaluate the advantages and problems of transpedicular screw instrumentation in 21 cases operated from June 1988 with minimum follow-up of 12 months. We concluded that transpedicular screw instrumentation offers better stability and earlier ambulation than conventional methods like Harrington and Knodt rod instrumentations. It, however, caused several problems such as screw breakage, screw loosening and recurrence of deformity. Therefore further study and efforts should be made to overcome those problems and to decrease the complications by technical improvement, additional anterior fusion or PLIF and strict postoperative immobilization.