STUDY DESIGN:: This is a retrospective study analyzing the results of Buck's operation for spondylolysis. OBJECTIVE:: To analyze the results of Buck's method as a treatment for symptomatic spondylolysis clinically and radiographically. And propose a new classification system of spondylolysis. SUMMARY OF BACKGROUND DATA:: 50 defects of 25 patients was classified into 4 subtypes and the bone fusion rate of each subgroups was analyzed. MATERIALS AND METHODS:: From March 1992 to March 2008, 50 defects of 25 patients with symptomatic spondylolysis were treated with Buck's method of direct repair. Surgical indication was (1) under 30 years of age, (2) with intractable low back pain without sciatica who did not response to conservative treatment for over 6 months, (3) without disc degeneration in lumbar MRI, (4) without instability in lateral flexion-extension view. Twenty males and five females with an average age of 21.2 years were followed up for an average 5 years 1 month. Clinical assessment using the Kirkaldy-Willis Criteria and radiographic assessment using the simple radiography and bone SPECT were performed. The pars interarticularis defects were classified into 4 subtypes in accordance with radiographical and intraoperative findings. RESULTS:: Clinically, there were 13 "Excellent", 9 "Good", 1 "Fair", and 2 "Poor" cases. 22 cases achieved Good to Excellent results. Radiographically, a total of 36 (72%) of the 50 defects showed union. There were no loosening of screws, but two patients showed screw breakages and nonunion postoperatively. There were no cases of postoperative complications except two cases of screw breakages. Pars interarticularis defects were classified into 4 subtypes- simple, atrophic, hypertrophic, and defect (gap) type. CONCLUSIONS:: It is suggested that Buck's operation, one of the method of treatment of spondylolysis is simple and has low complication rates. It is our conclusion that Buck's operation, which is a method of treatment for spondylolysis and mild spondylolisthesis when performed selectively in younger patients, can provide satisfactory results.