The objective of this paper was to discuss the main environmental factors determining overweight and obesity in adolescents, based on a critical review of the subject. The main national and international health databases, Medline/PubMed, Web of Science, SciELO, and Lilacs were searched including publications from 1975 to 2009. The following key-words and respective MeSH terms were used: "overweight", "obesity", "adolescence", "adolescents", "physical activity", "food intake". The findings showed that changes in dietary patterns in recent decades as the increased consumption of simple sugars, processed foods, and inadequate intake of fruits and vegetables have contributed directly to the weight gain in this population. In addition, the progressive reduction in physical activity associated with increased time spent with low-intensity activities like television viewing, playing computer and video games has contributed to the weight gain of adolescents. In conclusion, variables related to dietary pattern and physical activity should be prioritized interventions directed toward the prevention of obesity among adolescents.