The C677T (rs1801133) polymorphism of methylenetetrahydrofolate reductase (MTHFR) has been associated with bone status in some studies, but the results have been mixed. In order to have a better understanding of this issue, we performed a meta-analysis of studies about the association of the C677T polymorphism and bone mineral density (BMD). Eight studies analyzed the relationship with spine BMD. When their results were combined, individuals with TT genotype showed a small but significantly reduced BMD compared to those with TC and CC genotypes. The weighted mean difference (WMD) was 18.0 mg/cm2 (P = 0.001, 95% confidence interval [CI] 7.1-28.9), without statistical evidence for between-study heterogeneity (P = 0.28, I2 = 17%). Six studies analyzed femoral neck BMD. A test for heterogeneity was significant (P = 0.03, I2 = 56%). Individuals with TT alleles tended to have somewhat lower BMD, but the difference was not statistically significant. In random effects model, the WMD between the TT and TC/CC genotypes was 6.4 mg/cm2 (95% CI -7.8 to 21.2, P = 0.36). Total hip BMD was measured in four studies. They showed a significantly lower BMD in subjects with TT alleles: WMD 19.7 (95% CI 5.3-34.1) mg/cm2, P = 0.007, in comparison with TC/CC subjects. When we considered only studies on women, the WMD in BMD between TT and TC/CC genotypes was significant at the spine (22.1 mg/cm2, 95% CI 8.6-35.6; P = 0.001) and the femoral neck (15.5 mg/cm2, 95% CI 4.3-26.7; P = 0.007). There was no evidence for heterogeneity. The small number of studies did not allow a meaningful sex-stratified analysis of total hip BMD or a separate analysis of male data. In conclusion, the C677T polymorphism of the MTHFR gene is associated with small differences in BMD, at least in women.