PURPOSE: We analysed risk factors for failure of interlocking screws after femoral intramedullary nailing, and introduce tips for removing broken screw. MATERIALS AND METHODS: Seventy-two closed femoral shaft fractures were treated with interlocking nail. We compared 7 patients in whom interlocking screw breakage occurred (Group I) with 65 patients without breakage of interlocking screw (Group II). Analytic parameters were age, weight, level of fracture, degree of comminution, nail diameter. We used Mann-Whitney U test & Chi-sqare test for statistical analysis. RESULT: Upper one of distal interlocking screws was broken in 6 patients, both of distal screws were broken in one patient. All of the patients with broken screws had associated delayed union. The mean age of patients were 20 years in group I, 31 years in group II. The mean weight were 69.6 Kg in group I, 62.02kg in group II. Three patients had fractures in proximal half and four patients had fractures in distal half in group I. In group II, there were 25 proximal fractures and 40 distal fractures. There were 2 type I, 2 type II, 1 type III, 2 type IV fractures in group I, and 16 type I, 31 type II, 17 type III, 1 type IV fractures according to Winquist and Hansen classification. Nail diameters were 10mm in 4 patients, 11mm in 2 patients, 12mm in 1 patient for group I and 10mm in 8 patients, 11mm in 13 patients, 12mm in 25 patients, 13mm in 13 patients, and 14mm in 6 patients for group II. Age, weight, degree of comminution, nail diameter had statistically significant relation to the breakage of interlocking screw(p<0.05), but the level of fracture didn't(p>0.05). Broken screws were easily removed by advancing screw to medial compartment with S-pin and making short medial incision. CONCLUSION: It is suggested from our study that combination of parameters may have contributed to the failure of interlocking screw ; narrower diameter nail for comminuted fracture in young, active patients with more body weight. Inserting two screws have advantage over one screw.