ABSTRACT Objective: To characterize the adherence to the Mediterranean diet (MD) in students from elementary schools in Porto and Maia and analyze its association with sleep hygiene, physical activity, cardiometabolic risk, and school performance. Methods: This is a cross-sectional study with 891 Portuguese students: 455 boys (51%) and 436 girls (49%), aged between 9 and 11 years old (mean [M]=9.2, standard deviation [SD]=0.4), with an average weight of 35.9 kg (SD=8.1), average height of 1.4 m (SD=0.1), average body mass index (standardized BMI Z score for the pediatric age group) of 0.76 (SD=1.21); 59.5% of them had normal weight and 15.9% were obese. The students filled a questionnaire on the adherence to the Mediterranean Diet (Mediterranean Diet Quality Index in Children and Adolescents [KIDMED]), participated in a socio-demographic interview, and had their anthropometric data collected after their parents signed the informed consent form. Results: The results suggest high levels of adherence to the MD (77.6%) both in males and females. Using Pearson’s correlation coefficient, we found that the Z score was positively associated to cardiometabolic risk and the starting age of an extracurricular physical activity, and negatively associated to the average hours of sleep on a typical day both in males and females. We also identified a negative relation between KIDMED and the starting age of physical activity. Conclusions: This study has contributed to the knowledge of adherence to the MD among Portuguese elementary students and correlations with variables associated to a healthier lifestyle (MD, hours of sleep, and physical activity). Future studies should focus their attention on other countries and more heterogeneous samples.