The 5,10 methylene tetrahydrofolate reductase (MTHFR) is an enzyme that catalyzes the irreversible reduction of 5,10 methylene tetrahydrofolate into 5 methyl tetrahydrofolate. It is coded by a gene where several polymorphisms have been identified. The most common is the C677T polymorphism described as presenting an heterogeneous worldwide distribution and associated with different disorders such as cardiovascular and cancerous diseases. The aim of this work was to determine the allelic and genotypic frequencies of the C677T polymorphism among a Tunisian healthy population. The study concerned 185 subjects apparently healthy. It was carried out by the PCR/RFLP method, using the restriction enzyme Hinf I. The results has showed an allelic frequency of 17.8% with a genotype frequency of 5.4%. These values are intermediate between those observed in Africa and those observed in Western countries. They must be considered in the evaluation of the clinic significance of a predisposition to diseases.