The objective was to assess the association of the overall score and different items of the Mediterranean Diet Adherence Screener (MEDAS) questionnaire with academic achievement in Spanish university students. We hypothesized that university students with greater adherence to the Mediterranean Diet (MedDiet) would have better academic achievement. A cross-sectional study was performed involving 266 first-year students from the University of Castilla-La Mancha, Spain, during the 2017-2018 academic year. Adherence to the Mediterranean diet was evaluated with the 14-item MEDAS questionnaire. As an indicator variable for academic achievement, the average marks of the examinations required for access to Spanish universities were used. A total of 63 participants (23.6%) adhered to MedDiet recommendations. Analysis of covariance models showed that participants with higher adherence to the MedDiet had significantly higher scores on academic achievement than their peers with low adherence (P < .001) after controlling for potential confounders. Additionally, the evaluation of each item of the MEDAS questionnaire showed that a diet rich in olive oil, vegetables, fruits, legumes, fish and shellfish, and a low consumption of sweets and carbonated beverages were positively associated with academic achievement; nevertheless, wine intake was inversely associated. This study showed that Spanish university students had a low prevalence of good adherence to the MedDiet. Additionally, our results suggested that higher adherence to the MedDiet is associated with better academic achievement in Spanish university students. From a public health perspective and because of low adherence, it is important to continue to focus on promoting adherence to the MedDiet as part of a healthy lifestyle pattern to improve the academic performance of young university students.