5, 10 Methylenetetrahidrofolate Reductase (MTHFR) C677T and A1298C gene mutations has been describe as a cause of Recurrent Pregnancy Loss (RPL). It’s frequency in general Mexican population is 47%. This defect induces placentary thrombosis, diminishing fetal perfusion and cause abortion. The object of this study is to determine the frequency of this defect in a Mexican population with RPL. Observational, Descriptive and Cross-sectional, it was analyzed by using Microsoft Office Access and SPSS 11.0 (Statistical Package for the Social Sciences). We included 19 patients with RPL, from May 2003 to March 2005. Complete work up for RPL was done. Sample was taken by a frotis of bucal mucosa; it was sent to be analyzed through the Polymerase Chain Reaction method in the Millenova Immunology Laboratory (Chicago IL, USA), searching for MTHFR C677T and A1298C gene mutation. Of the 19 analyzed patients, 3(15.8%) of they were negative to the mutation and 16(84.2%) were positive; of these mentioned, 9(56%) patients had the heterocigote mutation and 7(43.7%) had the homocigote mutation. The C677T mutation was found in 12/16 (75%) of the patients, from these, 5/12 (41.6%) were homocigotes and 7/12 (58.4%) were in heterocigote state; the allelic variant A1298C, was presented in 4/16 (25%) patients, the homocigote state in 2/4 (50%) cases and the heterocigote state in 2/4 (50%). From the 16 positives patients for one of the two kind of mutations, only 7/16 (43.7%) underwent treatment to get pregnant, and of these, only 4/7 (57%) got pregnant, from which, 2/4 (50 %) got the homocigote genotype and 2/4 (50 %) had it in heterocigote state. The prevalence of MTHFR gene mutations in RPL patients was higher than the general Mexican population (84.2% vs. 47%). These findings suggest that in patients with recurrent pregnancy loss new diagnostic tools (thrombophilia panel) should be used. In this study 60% pregnancy rate was obtained after treatment.