We evaluated the reproducibility and validity of a 190-item semiquantitative food frequency questionnaire (FFQ) to be used in a large prospective study in the Athens area of Greece. Eighty persons, 42 men and 38 women, ages 25-67 years, completed a self-administered FFQ, followed by monthly 24-hour diet recalls and then a second FFQ 1 year after the first. Correlation coefficients measuring the reproducibility and validity of the FFQ indicate that the questionnaire is reproducible and provides a reasonably reliable measure of intake for many nutrients over a period of 1 year.