Objective: To assess the adherence to the Mediterranean dietary pattern in the population from a coastal region from north-east Spain and its relationship to diseases, applying the Mediterranean Diet Quality Index (M-DQI) validated by the use of several biomarkers. Design: Cross-sectional nutrition survey. Setting: Population-based random sample derived from the Catalan Nutrition Survey. Subjects: A total of 621 healthy adults. Results: The Catalan representative sample presented a mean M-DQI score of 6?6 (SD 2?3, median 7, range 0-14). The percentage of adherence to the Mediterranean diet was 53 %; 10 % of subjects showed high adherence to the Mediterranean diet, while only 2 % were categorized as poorest adherence. The plasma fatty acid profile of the Catalan sample progressed with perfect regularity throughout the index ranges. Both EPA and DHA presented a significant correlation to the M-DQI (r 5 20?410 for EPA and 20?360 for DHA). A significant increase in palmitic, oleic and a-linolenic acids and a significant decrease in stearic, linoleic and arachidonic acids content were also observed. The mean values for the M-DQI according to the clinical characteristics of the Catalan sample were also calculated. Conclusions: The M-DQI has been demonstrated a suitable tool for assessment of an individual's nutritional status according to the Mediterranean dietary pattern and for clinical purposes. Although the current diet followed in Catalonia seems to agree with the main characteristics of the Mediterranean diet, the promotion of the Mediterranean pattern should be reinforced in the Catalan population, especially among young people.