Bone defect occurs due to various causes, such as neoplasms, cysts, trauma, infection, congenital disease and surgical intervention. Autograft is generally considered to be the gold standard in bone graft surgery. But, allograft, xenograft and bone substitutes have been used because of complication and limited quantity of autograft. Calcium sulfate is one of the bone substitutes. We reviewed and analyzed 18 cases with bone defects that were treated with calcium sulfate from January 1997 to April 1997. We used the Osteoset' pellets that contained calcium sulfate 98%, produced by Wright Medical Technology Inc. in U.S.A., to fill defects in all cases. Except in 2 cases, autogenous cancellous bone from patients own iliac crest was mixed with calcium sulfate from 30% to 50%. Follow-up time averaged 13.7 months(range, from 12 to 15 months). The degree of absorption of calcium sulfate and new bone growth at conventional roentgenography was represented by percentage at each follow-up. The results were as follows. First, 8 weeks after operation, 93% of calcium sulfate was absorbed. Second, 6 months after operation, nearly 90% of new bone growth was observed. Third, until last follow-up, there was no noticeable complication, such as infection or foreign body reaction. We concluded that calcium sulfate might be on effective material for bone defects because of rapid absorption rate and easy recognition of new bone growth.