evidence: Pooled minor allele frequency (MAF) of 30 studies were 45% in Northern Han and 39% in Southern Han. To avoid a possible "false positive report," we further investigated the significant associations observed in the present meta-analysis using the FPRP test, which consolidated the results. In conclusion, MTHFR C677T polymorphism is associated with the increased risk of autism in China, especially in Northern Han. For those mothers and children who are generally susceptible to autism, prenatal folate and vitamin B12 may reduce the risk that children suffer from autism, especially in Northern Han populations. In the future, more well-designed studies with a larger sample size are expected. [...] In summary, the present meta-analysis is the first to provide refined current evidence of MTHFR C677T polymorphism with the increased risk of autism in Chinese Han. These results suggest that the MTHFR C677T polymorphism might be a risk factor for ASD in Chinese Han, especially in the north. For those mothers and children who are generally susceptible to autism, tailored nutrition treatment of prenatal folate and vitamin B12 may reduce the risk of having children with autism, especially in the north. Further studies with greater gene-environment statistical power are encouraged to verify our conclusions, taking into account more precise analysis of factors such as age, gender, and lifestyle factors in the development of autism.