Internet use has increased rapidly over the past 20 years, accompanied by a growing number of individuals whose Internet use has adverse effects on their lives. Yet no study to date has administered the Young\u27s Internet Addiction Test (IAT) in the United States, nor has the reliability been assessed in a U.S. population. Thus, we aimed to: (a) assess the reliability of the instrument and (b) examine sociodemographic characteristics associated with the Internet addiction score. Participants included young adults 21–28 years of age, the third generation of a 50-year longitudinal cohort, the New England Family Study. The mean weighted kappa across all 20 items of the instrument was 0.45 and the median was 0.46. To examine correlates of the addiction score, we examined age, gender, race/ethnicity, education, partnership status, employment, social support, and depression diagnosis. In the fully adjusted model, those with social support had −3.96 (95% CI: −6.52 to −1.41) lower Internet addiction scores on average compared to those without social support. Also, those with a depression diagnosis had 3.28 (95% confidence interval [CI]: 1.03–5.84) higher Internet addiction scores on average compared to those without a depression diagnosis. Study findings suggest that Young\u27s IAT had good reliability in a U.S. young adult population. Therefore, this measure can be a useful tool to measure Internet addiction in young adult populations in the United States. Future studies should examine the potential benefits of social support and depression treatment in Internet addiction among young adults in the United States
