Background:Body mass index (BMI) is inconsistently associated with the progression of low bone mass–related fractures. We conducted a systematic review and meta-analysis to summarize the evidence regarding the relationship between BMI and the risk of fracture in men and women separately. Furthermore, we analyzed the association between BMI and fracture risk in women compared with men.Methods:PubMed, EmBase, and the Cochrane Library were searched up to November 2015 to identify prospective cohort studies of low bone mass–related fractures. Prospective cohort studies that reported effect estimates of fracture risk for different BMI categories compared to normal weight were included. Relative risk (RR) and the ratio of relative risk (RRR) were calculated using a random-effect model to measure the relationship between BMI and fracture risk.Results:We analyzed 37 cohorts (32 articles), which included a total of 506,004 women and 118,372 men; overall, 38,200 incident cases were reported. Overall, a lower BMI was not associated with fracture risk in men (RR: 1.50, 95% confidence interval [CI]: 1.00–2.26; P = 0.051) or women (RR: 1.25, 95% CI: 0.97–1.62; P = 0.083). Although a higher BMI might play a beneficial impact in men (RR: 0.80, 95% CI: 0.69–0.93; P = 0.003), it has little effect in women (RR: 0.91, 95% CI: 0.74–1.11; P = 0.343). In addition, an increase in BMI by 5 kg/m2 decreased the risk of fractures in men (RR: 0.90, 95% CI: 0.83–0.98; P = 0.017) and women (RR: 0.85, 95% CI: 0.81–0.89; P < 0.001). Finally, there was no evidence of a sex difference in the RR for fractures between participants with different BMI categories compared with those with normal BMI. Finally, gender did not affect the risk of fracture for any category of BMI values.Conclusion:Higher BMI may affect the risk of fractures regardless of the sex. This association may be due to the interaction between the participants’ BMI and their bone mass density.