Objective To discuss the related factors of early pathological fracture after curettage of benign bone tumors in femoral shaft. Methods The clinical data of 47 patients with benign bone tumors in femoral shaft, treated by curettage with bone graft via the vastus lateralis approach from March 2004 to March 2011, were retrospectively analyzed. Thirteen patients of them presented with early pathological frac- ture after the curettage. |n fracture group, there were 13 cases, 11 males and 2 females, and the time from finishing curettage to fracture occurring ranged from 21 to 36 days. In non-fracture group, there were 34 eas- es, 23 males and 11 females. The following data of fracture group and non-fracture group were compared and analyzed, such as specific value of absolute width of tumor and transverse diameter of bone shaft, specific value of defect width of bone window and sagittal diameter of bone shaft, defect length-width ratio of bone window, defect morphology of bone window, classification of bone tumor, violence of causing injury and com- pliance to medical advice. Results The average defect length-width ratio of bone window in fracture group was 3.72±3.58, in non-fracture group was 2.67±6.35. For classification of tumor, in fracture group 1 case was in incubation period, 6 in active period, 6 in invasion period; in non fracture group 21 cases were in incubation period, 10 in active period, and 3 in invasion period. Four cases in fracture group had poor compliance to medical advice, and 9 in non-fracture group had good compliance. Between two groups, there were no sta- tistical differences in specific value of absolute width of tumor and transverse diameter of bone shaft, specific value of defect width of bone window and sagittal diameter of bone shaft, and defect morphology of bone window. Conclusion When defect length-width ratio of bone window is larger than 4, the classification of tumor causes expanded incisal edge, and the cortical bone was damaged extensively, there are more possibil- ities for pathological fracture. Key words: Femur; Bone neoplasms; Curettage; Fracture, spontaneous