BACKGROUND: the Mediterranean Lifestyle index (MEDLIFE) was developed as a questionnaire to capture adherence to an overall Mediterranean healthy lifestyle. The reliability of the MEDLIFE as an independent questionnaire must be evaluated prior its use in research studies. OBJECTIVE: to assess the inter-method reliability of the MEDLIFE as a short and independent research tool. DESIGN: the 28-item MEDLIFE questionnaire and a 142-item validated questionnaire (full-Q) from which we derived the 28-items MEDLIFE (MEDLIFE-derived) were administered simultaneously to 196 adults (mean age 41.4 ± 9.2 y) living in Madrid, Spain. The reliability was assessed by Kappa (k) statistics, intra-class correlation coefficients (ICC) and limits of agreement (LOA). RESULTS: overall correlation between the two instruments was 0.626. MEDLIFE had an acceptable ability to rank participants by MEDLIFE-derived from full-Q (ICC = 0.544). Absolute agreement showed very good concordance for 10.7% of the items evaluated; good to moderate concordance for most items, and fair concordance for 32.1% of the items. Intake of sweets, processed meats, low-fat dairy products and cereals were overestimated by MEDLIFE. About 38%, 15%, 12% and 10% of participants who scored 1-point for those items in MEDLIFE also scored 1-point in the MEDLIFE-derived respectively. Bland Altman's analysis showed that LOA ranged from -4.66 to 7.45 (mean = 1.40). CONCLUSION: the MEDLIFE is a valid instrument to measure overall adherence to the Mediterranean lifestyle in middle age adults from a Spanish population, and could be used as an independent questionnaire in clinical and epidemiological studies for such population. Its generalizability and predictive validity for clinical outcomes remains to be investigated.