Previous Mediterranean diet scores were simple to apply but may not be appropriate for non-Mediterranean populations. We developed a Mediterranean-Style Dietary Pattern Score (MSDPS) to assess the conformity of an individual's diet to a traditional Mediterranean-style diet. The MSDPS is based on the recommended intakes of 13 food groups in the Mediterranean diet pyramid. Each food group is scored from 0 to 10 depending on the degree of correspondence with recommendations. Exceeding the recommendations results in a lower score proportional to the degree of overconsumption. The sum of the component scores is standardized to a 0–100 scale and weighted by the proportion of energy consumed from Mediterranean diet foods. We applied the MSDPS to dietary data collected at the 7th examination of the Framingham Offspring Cohort and tested the content validity of the score against selected nutrients known to be associated with the Mediterranean-style dietary pattern. The mean MSDPS was 24.8 (range, 3.1–60.7). Participants with a higher MSDPS were more likely to be women, older, multivitamin users, to have lower BMI and waist circumferences, and less likely to be current smokers. The MSDPS demonstrated content validity through expected positive associations with intakes of dietary fiber, (n-3) fatty acids, antioxidant vitamins, calcium, magnesium, and potassium, and inverse associations with those of added sugar, glycemic index, saturated fat, and trans-fat, and the (n-6):(n-3) fatty acid ratio. The MSDPS is a useful instrument to measure overall diet quality according to the principles of a Mediterranean-style dietary pattern. J. Nutr. 139: 1150–1156, 2009.