Purpose: This cross-sectional study was conducted to investigate the prevalence of health risk behaviors by gender and grade and to examine the correlation between health risk behaviors and self-efficacy in early adolescents. Method: The sample of this study consisted of 1.693 early adolescents recruited from 7 middle schools in S-Gu, Seoul, Korea. Health risk behaviors were measured by the Youth Risk Behavior Surveillance Survey (YRBS). Self-Efficacy was assessed by General Self-Efficacy (GSE). Results: About a third of the subjects had experience in drinking behavior about 19.4% in cigarette smoking (including cases of just one or two puffs), 25.9% in physical fight, 29.1% in thought about killing themselves (suicide-related behavior), 1.5% in drug. More than a half (60.5%) experienced at least one health risk behavior. Female students were more likely to report drinking experience and suicide-related experience. Health risk behaviors were not significantly correlated with self-efficacy in early adolescents. Conclusions: Many early adolescents had experience in health risk behaviors in the past. The findings of this research suggest the necessity of intensive prevention programs in middle school to motivate and prepare students to avoid these behaviors. In addition, these results may help health professionals plan appropriate screening and counselling for health problems in early adolescents.