Background: Obesity is one of the main health concerns in adolescents. A sufficient level of knowledge about healthy eating can reduce the risk factors for this disease. The objective of the study was to determine the relationship between knowledge, attitudes and practices on healthy eating in an adolescent population of Lima (Peru). Methods: A cross-sectional study was carried out in 310 adolescents aged between 12 to 18 years from an educational institution. Knowledge, attitudes and practices were determined by means of a questionnaire developed according to the criteria proposed by the Food and Agriculture Organization of the United Nations (FAO). Tables of frequencies and percentages were used. Correlational analysis was performed using Spearman Rho test. A degree of significance of 5% was considered. Data analysis was performed through the IBM SPSS statistical software package. Results: 50.6% presented regular knowledge about healthy eating. 87.8% of the participants demonstrated favorable attitudes. Similarly, the largest proportion of the sample (69.1%) demonstrated adequate practices on healthy eating. A statistically significant positive correlation was found between the levels of knowledge with the attitudes and practices of the participants (rho = 0.197; p = 0.000) and (rho = 0.159; p = 0.005), respectively. Also, it was evidenced that attitudes are associated with levels of practices (rho = 0.427; p = 0.000). Conclusions: The results of the study show that adolescents present favorable levels of knowledge, attitudes and practices regarding healthy eating, however, the design and implementation of nutritional education programs in this age group is important.