Background and aims: An increasing number of people experience negative consequences from the excessive use of different Internet applications or sites (e.g., Instagram, League of Legends, YouTube). These consequences have been referred to as specific Internet Use Disorders (IUDs). The present study aims to examine the Fear of Missing Out (FoMO) on rewarding experiences with respect to specific Internet activities. FoMO has been found to mediate the link between psychopathology and symptoms of Internet Communication Disorder (ICD). However, the role of FoMO in other IUDs is controversial. Methods: The current study (N 5 7,990) consecutively screened in vocational schools) analyzed the associations between online-specific state-FoMO, general trait-FoMO, mental health, and IUD symptoms in a structural equation model. After testing the model for the entire sample of Internet users, it was analyzed separately for the two main user groups: Social Networking Site (SNS) users and gamers. Results: The proposed model explained 42.0% of the variance in IUD symptoms in the total sample, 46.8% for SNS users, and 32.8% for gamers. Results suggest that impaired mental health and high traitFoMO predict IUD symptoms. For both SNS users and gamers, trait-FoMO mediated the link between low mental health and IUD, whereas state-FoMO mediated the link between trait-FoMO and IUD in both user groups. Discussion: Our results partly support the theoretical model of specific IUDs, highlighting trait-FoMO as a predisposing fear of disconnection related to general mental health. Onlinespecific FoMO appears to contribute to problematic Internet use mainly because of its link to the general fear of disconnection. Moreover, the described mechanism seems to be comparable for both females and males. Conclusions: FoMO is a multidimensional construct underlying IUD symptoms related to the use of socially gratifying, but distinct Internet applications. FoMO and psychopathology should be targeted together in prevention and treatment plans of IUDs. Kulcsszavak: internet use disorder, I-PACE model, Fear of Missing Out, FoMO, social networking sites, gaming, structural equation modeling