The validity of a self-administered semi-quantitative food frequency questionnaire was evaluated for a group of 27 men and women aged 20 to 54. Intakes of 18 nutrients computed from the questionnaire were compared with those derived from 1-year diet records completed approximately 18 months earlier. The questionnaire estimates of mean nutrient intake were within 10% of the mean diet record measurements for 11 of the 18 nutrients evaluated, and the difference was less than 25% for all but one nutrient (total vitamin A). Correlation coefficients comparing unadjusted nutrient intakes measured by the two methods ranged from 0.38 (vitamin C) to more than 0.65 (total calories, total fat, saturated fat, polyunsaturated fat, oleic acid, and cholesterol). The overall mean of correlation coefficients comparing intakes of the 18 nutrients measured by questionnaire and by diet record was 0.60. Coefficients for macronutrients decreased somewhat after adjustment for age and gender or caloric intake. The data provide further evidence that a simple and relatively inexpensive questionnaire can provide useful information on dietary intake over an extended period.