OBJECTIVE: The authors investigated the efficacy of the calcium sulfate(OsteoSet(r) pellets) as an autograft extender when used to perform posterolateral lumbar fusions. PATIENTS AND METHODS: Twenty patients who underwent lumbar posterolateral arthrodesis for various spinal diseases between October 1999 and March 2000 were evaluated. Arthrodesis was performed by transpedicular screw fixation and bone grafting with a mixture of autograft + calcium sulfate in a 1:1 ratio. At time intervals of 1, 2, 3, and 6 months, postoperative radiographs were obtained to review the resorption of calcium sulfate and the evidence of fusion. A modified Lenke scale was used to assess the status of the fusion. RESULTS: At 2 months after operation, the average modified Lenke scale score for the OsteoSet(r) pellets group was 3.8. However at 6 months after operation, the average modified Lenke scale score for the OsteoSet(r) pellets group was 1.8. Resorption of calcium sulfate pellets was revealed in all cases at 6 months after surgery. CONCLUSION: It is presumed that a combination of calcium sulfate and autograft can play a role as an effective autograft extender in the posterolateral spinal fusion.