Abstract : Background: In countries undergoing rapid urbanization and economic growth like Bahrain, changes in lifestyle and dietary habits are observed especially among adolescents, with a rise in obesity and other nutrition-related chronic diseases. Unhealthy dietary habits and an increase in the prevalence of overweight and obesity among the adolescent population in Bahrain have been reported. The continuing increase in the prevalence of obesity in Bahrain suggests the current measures to prevent and control obesity are inadequate. Prevention is now crucial, and adolescents should be a priority target, because of conducive eating patterns and lifestyles. Establishing healthy nutrition and physical activity habits in young boys and girls is considered to be an important factor in maintaining healthy lifestyle patterns that can persist through adolescence and into adulthood. Objectives: 1- To assess students' nutritional status using weight and height measurements, 2-To determine the eating habits and the lifestyle of public secondary school students in Bahrain and the difference of these habits between male and female 3- To explore the possible relationship between obesity and eating habits and lifestyle among students in public secondary schools in Bahrain. Aim: To provide base-line data for school Health Nutritional Program in Bahrain, on which a future modified school nutrition program can be implemented in order to promote healthy eating habits in schools, and improve the overall nutritional status of Bahraini adolescents. Methods: A cross-sectional study comprising of 735 students (339 males and 396 females), ages 15-18 years, selected by multistage random sampling from government secondary schools in all five governorates of Bahrain. Information on dietary habits and lifestyle were obtained by self administered questionnaire. Anthropometric measurements (height and weight) were taken and obesity was determined by using body mass index (BMI). Results: Eating habits of Bahraini adolescents showed excessive ingestion of sweets, chocolates, soft drinks, canned fruit juices, snacks and fast foods especially among females. A large percentage (56%) of adolescents were not eating breakfast regularly, however skipping three meals were more popular among females than males (breakfast P=0.000, lunch P=0.001 and supper P=0.000). High percentage of adolescents (73.5%) was physically active and practicing sports, especially males. Gender difference was significant with practicing sports during school hours and outside school, however females' participation in sports activity inside the school was more than outside school (P=0.026). The prevalence of overweight and obesity were higher among females adolescent (17.4% and 19.4% respectively) than males (15.8% and 13.7% respectively). Since the prevalence of underweight was very low in both genders (8.6% of males and 2.3% of females) the sample was divided into two groups, overweight and obese (BMI ≥85th percentile) and non-obese group (BMI <85th percentile), with this category overall prevalence of overweight and obese group was higher in females adolescent (36.9%) than males (29.5%). Of the determinants of obesity including socio-demographic variables, parents' level of education especially maternal literacy was directly associated with increased overweight and obesity among both genders. The results showed no significant association between unconventional dietary habits and lifestyle with the prevalence of overweight and obesity among Bahraini adolescents. However, among adolescent males, fast food habits showed significant association between consuming large burger size (P=0.003) and nutritional status. Negative significant results showed among male adolescents between snaking habits and nutritional status. Conclusion: Unhealthy dietary habits were observed, along with increasing prevalence of overweight and obesity among adolescents 15-18 years in Bahrain, especially among females. These findings indicate an urgent need for prevention program to tackle these problems. To ensure a healthy future, a comprehensive school-based nutrition program must become a national priority. Such a program should be an integral part of the school health programs and applied to the students from preschool through secondary school. Key policies that schools can use to improve students' nutrition and increase physical activity are suggested along with resources that can help schools to strengthen and implement these policies.