Objective: The Mediterranean diet (MD) pattern has important health benefits; however, it seems that Spanish school-aged children have been abandoning this healthy pattern recently. We aimed to identify psychopathological, anthropometric and sociodemographic factors that may influence the risk of low MD adherence. Design: Longitudinal study in three phases. MD adherence was assessed using the Krece Plus food questionnaire and psychopathological symptoms using the Screen for Childhood Anxiety Related Emotional Disorders, Children's Depression Inventory, Youth's Inventory-4 and Eating Disorder Inventory-2. Anthropometric data were collected in the first and third phases. Settings: All five representative areas in Reus, Spain. Subjects: Adolescents (n 241). Results: Regardless of past and current BMI, socio-economic status was a protective factor for low MD adherence (OR = 0·805, P = 0·003) and a risk factor for high BMI (OR = 0·718, P = 0·002; OR = 0·707, P = 0·001). Regardless of socio-economic status, depression was involved with risk of low adherence (OR = 1·069, P = 0·021). Girls with lower MD adherence presented significantly higher scores for eating disorders measured using the Eating Disorder Inventory-2 (low adherence, mean 18·9 (SD 13·5); high adherence, mean 8·9 (SD 9·0), P = 0·020) and the Youth Inventory-4 (low adherence, mean 5·2 (SD 4·3); medium adherence, mean 3·6 (SD 3·2), P = 0·044). They also presented higher depression symptoms (low adherence, mean 17·7 (SD 9·6); medium adherence, mean 12·3 (SD 7·2), P = 0·01) than girls with high adherence. Conclusions: The results highlight the influence of psychosocial factors on levels of MD adherence. These factors need to be taken into account when developing prevention and health promotion initiatives.