Introduction: Defining dietary patterns by factor analysis is an alternative approach to dietary assessment. Our aim was to assess both the validity and reproducibility of major dietary patterns, based on data from obtained using a food frequency questionnaire (FFQ) among Tehranian women. Materials and Methods: Using random sampling of registries, women aged 18 to 45 years were selected. The first food frequency questionnaire (FFQ1) was completed by trained interviewers. We asked our subjects to record their diet, 2 days per month, during 1 year. At the end of the year, a second FFQ (FFQ2) was again completed by interviewers. By conducting factor analysis, dietary patterns were identified. Results: Two factors were detected in the 3 sets of data. For assessing reproducibility, the Pearson correlation was assigned to detect the correlations between factor scores measured in FFQ1 and FFQ2.  The reliability correlations for the factor scores between the 2 FFQs ranged from -0.05 to 0.11, for the 2 factors. The validity correlations for the factor scores between the FFQ1 and dietary records (ranged from -0.16 to 0.29, for the 2 factors) and between FFQ2 and dietary record (ranged from 0.02 to 0.11 for the 2 factors) were detected. Conclusion: Our results indicate that identification of dietary patterns, using a food frequency questionnaire, in this group was not a reproducible or valid method.