Background and objectives: Although there has been a remarkable increase in screen time among children over recent years, the literature includes contradictory reports on its effects of the individuals' health. In this regard, the present study was an attempt to figure out the effects of heavy screen time on the health of secondary school-aged children in Duhok city, Kurdistan-Iraq. Methods: A cross-sectional study was conducted on 850 secondary school students aged 14- 18 years, from September 2022 to September 2023 in Duhok secondary schools. Data about screen viewing were gathered through a questionnaire. then data were analyzed via SPSS (version 25.0). Chi-square were used and 0.05 was set a level of significant. Results: The students aged 14-18 years, with the largest group being 18 years of age (38.4%). Most of the students (59.4%) were females. Grade 12 students were the largest group (57.3%). Most of them (76.2%) were from middle-income families and (65.4%) had healthy body mass index. Significant associations were found between the students' screen time and their age (P-value<0.001), gender (p-value<0.001), parents' education (P-value<0.001), parents' occupation (P-value<0.05), and socioeconomic status (p-value=0.014). Moreover, significant associations were found between their screen time duration and their medical problems (P-value<0.001), previous surgical operation (p-value=0.008), mood during the day (P-value<0.001), relationship with parents (p-value=0.003), sleep difficulties (p-value=0.002), and eating during screen viewing (p-value<0.001). Conclusions: Most adolescence in Duhok city have excessive screen time (more than two hours) in which affects their health and quality of life adversely. Health practitioners and families should consider these factors while designing and implementing adolescent health promoting programs.