The sixth edition of the Dietary Guidelines for Americans (DGA) was released in January 2005, with revised healthy eating recommendations for all adult Americans. We developed the 2005 Dietary Guidelines Adherence Index (DGAI) as a measure of adherence to the key dietary intake recommendations. Eleven index items assess adherence to energy-specific food intake recommendations, and 9 items assess adherence to "healthy choice" nutrient intake recommendations. Each item was scored from a minimum of 0 to a maximum of 1, depending on the degree of adherence to the recommendation. A score of 0.5 was given for partial adherence on most items or for exceeding the recommendation for energy-dense food items. The DGAI was applied to dietary data collected at the fifth examination of the Framingham Heart Study Offspring Cohort. The mean DGAI score was 9.6 (range 2.5-17.50). Those with higher DGAI scores were more likely to be women, older, multivitamin supplement users, and have a lower BMI and less likely to be smokers. The DGAI demonstrated a reasonable variation in this population of adult Americans, and by design this index was independent of energy consumption. The DGAI also demonstrated face validity based on the observed associations of the index with participant characteristics. Given these attributes, this index should provide a useful measure of diet quality and adherence to the new 2005 Dietary Guidelines for Americans.