Introduction: Adolescence is a period of physical, psychological, cognitive and emotional changes, where autonomy from parental control is demanded. Adolescents are often self-discovering, frequently adopting sexual and drug exploration behaviors. As a result, health status in both adolescence and adulthood can be influenced. Methods: A pre-validated questionnaire was used to evaluate the prevalence and possible determinants of risky behaviors in a convenience sample of 8th grade students attending several Gaia schools in 2011-2012. Results: The present study included 375 students. From these students, 20.3% had experimented with tobacco and 23.7% of those used to smoke regularly. Regarding alcohol intake, 43.2% had experimented and 8% had at least one episode of alcohol intoxication. Consuming other drugs (3.7%) was associated with tobacco use. Sexual activity was reported in 9.9%, and 8.5% of the sample reported regular acknowledged condom use. Parental divorce, older siblings with academic failure, self-academic failure and self-perceived bad school integration were significantly associated with substance abuse behaviors and engagement in early sexual activity. Misconceptions regarding the risks of tobacco and alcohol use/misuse were the strongest predictors of experimentation and abuse. Conclusion: Adolescents are at-risk for tobacco, alcohol use, drug experimentation and early engagement in sexual activity. Risk factors are students with past school retention, lack of parental support structure, especially regarding those with older siblings who present past academic failure and a lack of study habits. We suggest that this information can be used to tailor interventions and to help implement preventive strategies.