OBJECTIVE To compare and evaluate the reliability of several indexes of adherence to the Mediterranean diet. DESIGN The ten indexes included in the analysis were: Mediterranean Diet Score (MDS), Mediterranean Score (MS), Dietary Score (DS), Mediterranean-Dietary Quality Index (Med-DQI), Mediterranean Dietary Pattern adherence index (MDP), Mediterranean Adequacy Index (MAI), Mediterranean Style Dietary Pattern Score (MSDPS), Mediterranean food pattern PREDIMED Study (MeDiet-PREDIMED), relative Mediterranean diet (rMED) and Cardioprotective Mediterranean diet index. Factor analysis using the correlations between indexes was applied. The correlation with factors and the reliability coefficient were calculated. SETTING A total of 324 healthy undergraduates at the University of Barcelona, Spain, were surveyed. RESULTS The highest correlations were observed between MDP adherence index and MAI (0·82); MAI and MSDPS (0·80); and MDS and rMED (0·77). Factor analysis showed a hidden common factor that explained over 70 % of the variability (71·03 %). This factor is understood as 'adherence to the Mediterranean diet'. The indexes that showed the highest correlation with this factor were Med-DQI (0·85), MDS (0·84), rMED (0·80) and MAI (0·80). These indexes showed acceptable performance in measuring the adherence to the Mediterranean diet. The components that correlated strongly with this factor were monounsaturated-to-saturated fatty acid ratio (MS ratio), fruit and vegetables. Furthermore, a second common factor was found explaining 18 % of the variability. This second factor is highly positive related to dairy products and lean meat, and negative related to MS ratio. CONCLUSIONS The indexes showed satisfactory performance in assessing adherence to the Mediterranean diet. However, in order to improve the reliability and concordance between the indexes, further studies are required to select the components, the number of components, and the scoring criteria of the indexes to improve their internal consistency.