Objective To evaluate the therapeutic results of percutaneous injection of autogeous bone marrow for simple bone cyst and to analyze the prognostic factors of the treatment. Methods From March 2000 to June 2005, 31 patients with simple bone cysts were treated by percutaneous injection of autogeous bone marrow. Of 31 patients, there were 18 males and 13 females, aged 5 years and 7 months to 15 years. The locations were proximal humerus in 18 cases ,proximal femur in 7 cases and other sites in 6 cases. Two cases were treated with repeated injections. The operative process included percutaneous aspiration of fluid in the bone cysts and injection of autogenous bone marrow aspirated fromposterior superior iliac spine. The mean volume of marrow injected was 40 ml(30-70 ml).Results No complications were noted during treatment. Thirty patients were followed for an average of 2.2 years(1.5 years) with 2 cases out of follow-up. After one injection of bone marrow, 9 cysts(29.0%) were healed up completely, 7 cysts(226%)basically healed up,13 cysts (41.9%)healed up partially and 2 (6.5%) had no response.The satisfactory and effective rates were 67.7% and 93.5% respectively. There was significant difference between active stagegroup and resting stage group(P＜0.05). There were no statistically significant difference in therapeutic results between groups of different ages, lesion sites or bone marrow hyperplasia(Pgt;0.05). Conclusion Percutaneous injection of autogeous bone marrow is a safe and effective method to treat simple bone cyst, but repeated injections is necessary for some patients. The therapeutic results are better in cysts at resting stage than those at active stage.