To design and develop a questionnaire that can account for an individual's adherence to a Mediterranean lifestyle including the assessment of diet and physical activity patterns, as well as social interaction. The Mediterranean Lifestyle (MEDLIFE) index was created based on the current Spanish Mediterranean food guide pyramid. MEDLIFE is a twenty-eight-item derived index consisting of questions about food consumption (fifteen items), traditional Mediterranean dietary habits (seven items) and physical activity, rest and social interaction habits (six items). Linear regression models and Spearman rank correlation were fitted to assess content validity and internal consistency. A subset of participants in the Aragon Workers' Health Study cohort (Zaragoza, Spain) provided the data for development of MEDLIFE. Participants (n 988) of the Aragon Workers' Health Study cohort in Spain. Mean MEDLIFE score was 11·3 (sd 2·6; range: 0-28), and the quintile distribution of MEDLIFE score showed a significant association with each of the individual items as well as with specific nutrients and lifestyle indicators (intra-validity). We also quantified MEDLIFE correspondence with previously reported diet quality indices and found significant correlations (ρ range: 0·44-0·53; P<0·001) for the Alternate Healthy Eating Index, the Alternate Mediterranean Diet Index and Mediterranean Diet Adherence Screener. MEDLIFE is the first index to include an overall assessment of lifestyle habits. It is expected to be a more holistic tool to measure adherence to the Mediterranean lifestyle in epidemiological studies.