Purpose: This study was done to identify the state of internet addiction and to investigate the relationships among internet addiction, depression and suicidal ideation in adolescents. Method: Participants were 1,670 high school students in an urban city. The Internet Addiction Scale was used to measure internet addiction, the DISC-MDD-SQ was used to measure depression, and the Suicidal Ideation Questionnaire-JR was used to measure suicidal ideation. Result: 38.1 % of participants were perceived to be in the early stages of internet addiction and 1.5% reported heavy addiction. Overall the internet addiction scale score was 37.57(${pm12.52}$). The differences of internet addiction in sample characteristics were found to be significant in rank in class. The differences in DISC-MDD-SQ and IAS scores among the states of internet addiction were statistically significant. The level of internet addiction correlated positively to the level of depression and suicidal ideation. Conclusion: Based upon these findings, there were significant positive correlations among Internet addiction, depression, and suicidal ideation in adolescents. As schools are often the first line for the identification of potential life-threatening behaviors, nurses, especially school-based health professionals, need to be cognizant of measures and procedures for the assessment of Internet addiction, depression, and suicidal ideation.