INTRODUCTION: Fractures of femoral fracture are among the most common fractures encountered in orthopedic practice. Intramedullary nailing is the treatment choice for femoral shaft fractures in adults. The objective of this article is to determine the effects of reamed intramedullary nailing versus unreamed intramedullary nailing for fracture of femoral shaft in adults. METHODS: Cochrane Central Register of Controlled Trials (October 2010), PubMed (October 2010) and EMBASE (October 2010) were searched. Randomized and quasi-randomized controlled clinical trials were included. After independent study selection by two authors, data were collected and extracted independently. The methodological quality of the studies was assessed. Pooling of data was undertaken where appropriate. RESULTS: Seven trials with 952 patients (965 fractures) were included. Compared with unreamed nailing, reamed nailing was significantly lower reoperation rate (RR 0.25, 95% CI 0.11-0.59, P = 0.002), lower non-union rate (RR 0.20, 95% CI 0.05-0.77, P = 0.02) and lower delay union rate(RR 0.30, 95% CI 0.14-0.64, P = 0.002). There was no significant difference when comparing reamed nailing with unreamed nailing for implant failure (RR 0.51, 95% CI 0.16-1.61, P = 0.25), mortality(RR 0.94, 95% CI 0.19-4.58, P = 0.94) and acute respiratory distress syndrome(RR 1.53, 95% CI 0.37-6.29, P = 0.55). Unreamed nailing was significantly less blood loss (SMD 119.23, 95% CI 59.04-180.43, P = 0.0001). CONCLUSION: Reamed intramedullary nailing has better treatment effects than unreamed intramedullary nailing for shaft fracture of femur in adults.