Introduction: Childhood overweight and obesity, major public health concerns, show a drastically rising tread worldwide. Associated with an increased risk of developing cardiovascular and endocrine problems, overweight children are more likely to be overweight adults.  This study was done to evaluate the prevalence of overweight, obesity, and underweight among high school students in Sanandaj, Kurdistan, Iran. Materials and Methods: This study was performed in 2007 on 694 students from Sanandaj high schools. Socio-demographic information was collected using a questionnaire, completed during interviews. Weight and height were measured. Body mass index (BMI) was calculated and overweight/obesity was defined using age- and sex-specific BMI cut-off points, proposed by the World Health Organization Expert Committee on Physical Status (World Health Organization, 1996). Children with BMI-for-age at or above the 95th percentile, between 85 and 95th percentile and less than 5th percentile were considered as being obese, overweight and underweight respectively. Descriptive and analytical statistics were used to analyze the data. Results: The average of BMI was 20.7 and prevalences of overweight, obesity and underweight were 11.2, 3.2 and 7.6 % respectively. Levels of overweight/obesity (14.4%) differed significantly between boys (18.2 %) and girls (10.7 %). The highest percentage of overweight/obesity (20%) was found among 14-years olds. Boys showed a consistent decrease in overweight/obesity with increasing age, a trend not demonstrated in girls. Conclusion: Results indicated that the prevalence of overweight/obesity among high school students in Sanandaj is near national averages for adolescents. Overweight/obesity were observed more in boys than in girls. As a group, girls demonstrate a lower prevalence of obesity (1.1%) when compared to national averages. Based on the results of this study, 22 percent of the high school students in Sanandaj have inappropriate weight, which calls for appropriate intervention programs.