Abstract: Motorcyclists are more prone to crash injuries than car drivers because motorcycles are unenclosed, leaving riders vulnerable to contact hard road surfaces. This study was conducted based on safety helmet issues among adolescents. Theory on behavioral sciences like Theory of Planned Behaviour (TPB) is useful in understanding why adolescent motorcyclist regardless helmet safety usage. A cross-sectional study was carried out with a sample size of 288 adolescents was chosen in this study. The data collected were carried using a questionnaire survey. The descriptive analysis shows, more than half of respondents are those aged between 17 to 18 years old. Majority (80%) of them do not have motorcycle licenses. This means that they are riding a motorcycle without a basic knowledge of road traffic regulations. Over 65% respondents were riding a motorcycle every day or almost daily during the last 12 months. The correlation analysis shows, there are strong positive relationship between intention and behaviour of respondent. Sometimes they wear helmets, however rarely to wear helmets especially in a short distance (less than 2 km). In addition, the hierarchical multiple regression analysis shows all variables including descriptive norm were found significant (p<0.05), except perceived behaviour control shows insignificant relationship to intention to use a safety helmet. As conclusion, attitude, subjective norm and intention remained a significant predictor of behaviour. However, perceived behaviour control and descriptive norm were not significant in predicting such behaviour (safety helmet usage).