The prevalence of musculoskeletal pain among students is noticeable. Different studies have reported the prevalence rate above 40%. The aim of this study was to investigate the prevalence of musculoskeletal pain among middle school students in Sanandaj, Iran, and discovering the causes of the pain among them. The study was performed on boy and girl students in secondary schools. 735 students in age range of 12 to 15 years was selected and some information about their school bags, chair type, and the number of hours watching TV or working on computer was obtained using a questionnaire. Weight, height, and BMI of students were measured. Body mapping revealed that musculoskeletal pain is appeared in the neck, shoulders, hands and wrists, back, elbows, back, hips, knees, and feet and ankles. The prevalence of musculoskeletal pain among schoolchildren was found to be 67%. The prevalence of musculoskeletal pain had a significant relationship with sex, type of school bag, the number of hours watching TV and working on computer. The prevalence of musculoskeletal pain had no significant correlation with chair type used at school. The study showed that musculoskeletal pain is highly prevalent among the students. We need to teach the students to improve ergonomics and preventive behaviors in order to modify unsuitable conditions for students and teachers at school in taking steps. Risk factors for musculoskeletal pain in children are sex, type of school bags, and time spent watching TV and working on computer .