Background: The aim of this study is to measure the level of internet addiction among high school adolescents and to determine the relationship between their time spent on the internet and the back and neck pain and eye health problems they experience.Methods: The study is a simple cross-sectional descriptive study. 8926 high school students participated in the study. Students were selected by cluster sampling method pursuant to their gender, school type, and grade distributions. Young's short internet addiction test (IAT) that was adapted to Turkish was utilized. Results: The average internet addiction score of the students was 26.88 ± 8.80. While the ratio of students with a high risk of addiction was 44.3% (n=3950), the ratio of those, who were addicted, was 15.7% (n=1400). A significant positive correlation was found between the addiction level and the lower back, neck pain and eye disorders. (p<0.001; p<0.001; p<0.001) The smartphone possession rate of students was 96.4% (n=8606). There was a significant positive correlation between having a smartphone and the level of addiction, neck pain, and eye complaints. (p=0.005; p=0.002; p=0.003, respectively)The ratio of students, who have a computer at home, was 79.8% (n=7122). Eye complaints were found to be significantly higher in those, who had a computer at home (p<0.001).Conclusion: Internet addiction is an important and common problem among adolescents. Internet addiction increases, as the age of adolescents increases. Smartphones are the most important risk factor for the spread of internet addiction. Internet addiction leads to muscle-joint pain, and eye-related symptoms.