BACKGROUND AND AIMS Validated dietary assessment methods specific to population and food habits are needed to conduct randomized clinical trials evaluating the efficacy of the Mediterranean diet in primary and secondary prevention of cardiovascular disease. Therefore, the aim of our study was to assess the reproducibility and the relative validity of a French language semi-quantitative food frequency questionnaire (FFQ) focused on the Mediterranean diet within the population of Quebec. METHODS AND RESULTS Fifty-three participants aged 19-86 years with and without coronary heart disease were recruited, and randomized in 3 groups in a crossover design where the sequence of administration of two FFQs and a dietary record (DR) differed in each group. The FFQ includes 157 food items and was designed to measure food intake over one month. It was administered twice 3-5 weeks apart to assess reproducibility and was compared to a 12-day DR to assess validity. For reproducibility (n = 47), intraclass correlation coefficients (ICCs) for energy and 33 nutrients ranged from 0.38 to 0.91 (mean 0.63). For validity, the Pearson's correlation coefficients between the DR and the FFQ pre-DR ranged from 0.26 to 0.84 (mean 0.55) and ICCs ranged from 0.25 to 0.84 (mean 0.54). As for the DR and the FFQ post-DR, the Pearson's correlation coefficients ranged from 0.36 to 0.83 (mean 0.55) and the ICCs ranged from 0.36 to 0.83 (mean 0.53). CONCLUSION This FFQ demonstrates good reproducibility and validity for most key nutrients of the Mediterranean diet for the Quebec population.