Objective Compulsive Internet Use (CIU) has been linked to lower wellbeing, especially among adolescents. Yet, questions regarding the directionality of this association remain unanswered: CIU may influence wellbeing and vice versa. Theoretically, both directions are plausible, yet so far no studies have examined the directionality of these effects among adults. This article aims to shed light on the directionality of the relation between CIU and both positive and negative wellbeing, using a prospective, longitudinal sample of adults (n = 398). Methods Over the course of four years, participants completed five assessments of their CIU and both positive and negative indicators of wellbeing. Participants were married couples who were recruited in the municipalities where they were married. Results CIU predicted increases in depression, loneliness and stress over time, and a decrease in happiness. No effect of CIU on the change in self-esteem was found. Further, happiness predicted a decrease in CIU over time. Conclusions The results suggest CIU lowers wellbeing. This is important given that lowered wellbeing may affect health. Happiness is suggested to be a buffer for developing CIU. © 2014 Elsevier Ltd. All rights reserved.