IntroductionProblematic online behaviors, including sexting, cyberbullying, and Internet gaming disorder (IGD), were associated with a higher risk of self-harm among adolescents. However, the independent effect on self-harm brought by each problematic online behavior remains unknown. MethodsThis cross-sectional nationwide survey investigated a representative sample of 8446 Taiwanese adolescents (49.7 % female, mean age = 15.4 ± 1.8, ranging from 10 to 18) in the summer of 2021. We used self-reported questionnaires to assess adolescents' problematic online behaviors. 18-item Risk-Taking and Self-Harm Inventory was applied to evaluate their self-harm risks. Adolescents with score ≥ 7 were considered self-harm identified. Multivariate regression analyses were performed to investigate the association between problematic online behaviors and self-harm risks. ResultsThe prevalence of sexting, cyberbullying victimization, cyberbullying perpetration, and IGD was 1.3 %, 1.1 %, 0.9 %, and 0.7 %, respectively. Adolescents with sexting were associated with higher self-harm scores (β = 4.30, 95 % CI [3.35, 5.25]), so did adolescents with IGD (β = 3.33, 95 % CI [1.96, 4.71]), cyberbullying perpetration (β = 2.61, 95 % CI [1.03, 4.20]), and cyberbullying victimization (β = 1.40, 95 % CI [0.04, 2.76]). Also, sexting (OR = 5.16, 95 % CI [3.26, 8.07]) and IGD (OR = 3.11, 95 % CI [1.50, 6.15]) were associated with increased odds of identified self-harm behaviors. ConclusionsSexting, cyberbullying victimization, cyberbullying perpetration, and IGD were all independently associated with an increased self-harm risk among adolescents. Among them, sexting was shown to be the most robust risk factor of identified self-harm behaviors. To prevent self-harm among adolescents, it is important to identify youth involved in problematic online behaviors, especially sexting.