Background and aims: Internet Use Disorders (IUDs) are emerging as a societal challenge. Evidencebased treatment options are scarce. Digital health interventions may be promising to deliver psychological treatment to individuals with IUDs directly in their online setting. The aim of this study was to evaluate the efficacy of a digital health intervention for IUDs compared to a waitlist control group (WCG). Methods: In a two-armed randomized controlled trial, N 5 130 individuals showing IUDs (Internet Addiction Test; IAT .49) were randomly allocated to the intervention group (IG; n 5 65) or WCG (n 5 65). The intervention consisted of 7 sessions based on cognitive behavioral therapy. The primary outcome was IUD symptom severity measured via the IAT at post treatment 7 weeks after randomization. Secondary outcomes included IUD symptoms (Compulsive Internet Use Scale; CIUS), quality of life, depressive and anxiety symptoms, and other psychosocial variables associated with IUDs. Results: Participants were on average 28.45 years old (SD 5 10.59) and 50% identified as women, 49% as men, and 1% as non-binary. The IG (n 5 65) showed significantly less IUD symptom severity (IAT) (d 5 0.54, 95% CI 0.19.0.89) and symptoms (d 5 0.57, 95% CI 0.22.0.92) than the WCG (n 5 65) at post-treatment. Study attrition was 20%. Effects on all other secondary outcomes were not significant. On average, participants completed 67.5% of the intervention. Discussion and Conclusions: A digital health intervention could be a promising first step to reduce IUD symptom severity.  Kulcsszavak: digital health intervention, internet use disorders, randomized controlled trial, cognitive behavioral therapy for IUDs, online CBT, guided self-help