“Internet addiction” was first described in the dial-up era (Young KS. Psychol Rep 1996;79:899-902), with the prevalence steadily increasing with more widespread internet access. Five years ago, a meta-analysis reported a global prevalence of 6.0% (Cheng et al. Cyberpsychol Behav Soc Netw 2014;17:755-760). More recent estimates have found a prevalence of 17.7% among adolescents in rural Japan (Kojima et al. Psychiatry Clin Neurosci 2019;73:20-26), and 38.2% among university students in Japan (Kitazawa et al. Psychiatry Clin Neurosci 2018;72:531-539). The range in prevalence is largely due to a lack of consensus on diagnostic criteria, which in itself is a reflection of a more fundamental controversy: is Internet overuse an “addiction” or only problematic?