The aim of the present study was to describe Mediterranean diet adherence within a population of adolescents and to analyse the association of multiple factors with adherence. This included a consideration of diverse physical and mental health indicators. The present study was conducted with a representative sample of 761 adolescents (14.51 ± 1.63 years) from 25 educational centres in a northern region of Spain. Mediterranean diet adherence was evaluated, alongside their health-related quality of life, self-esteem, body image satisfaction, body mass index, physical activity level, maximum oxygen consumption, hours of nightly sleep, sociodemographic factors and academic performance. Forty-nine percent of the adolescent population reported high Mediterranean diet adherence. The female gender and higher levels of physical activity were found to be predictive factors of adherence to the Mediterranean diet. In addition, maximum oxygen consumption, the presence of environments favourable towards physical activity engagement and higher self-esteem were also predictive in females, whilst better academic performance and more nightly sleep were additional predictors in males. The associations found between Mediterranean diet, and other health indicators and habits, highlight the need to develop promotion strategies from an inter-disciplinary and transversal standpoint.