Objectives: The aim of this study was to investigate the relationship between age at cigarette smoking initiation and smoking level among adolescent current smokers. Methods: In 2007, students from one or two classes of the 10th or 11th grade were randomly selected using the probability proportional to size sampling method. In total, 743 current smokers were included. Multiple logistic regression was used to determine the association between age at smoking initiation and smoking level as either frequent, daily, or heavy smokers. Results: The adjusted odds ratios for each smoking level were significantly higher for younger ages of smoking initiation than those for older ages of initiation were (p for trend <0.001). Compared with the students who started smoking in grades 10 to 11, the adjusted odds ratios for frequent, daily, and heavy smokers increased from 2.24 (95% confidence interval [CI], 1.30 to 3.87) to 3.90 (95% CI, 2.02 to 7.56), from 1.56 (95% CI, 0.92 to 2.62) to 3.17 (95% CI, 1.70 to 5.92), and from 2.56 (95% CI, 1.21 to 5.42) to 5.67 (95% CI, 2.61 to 12.30) with younger ages of smoking initiation. Conclusions: Smoking frequency and amount were closely associated with age at smoking initiation. Therefore, smoking prevention programs should be initiated from the young adolescent period.