Abstract: To be a trustworthy partner, people need self-control. People infer others’ level of self-control from behavioral cues, and this perception influences how much they trust others. Exhibiting compulsive Internet use (CIU) might provide such cues. This research examined whether and how CIU affects perceptions of self-control and trust in a partner. In an experimental study, we manipulated CIU in descriptions of strangers and found that participants in the CIU condition judged the other to have lower self-control and trusted them less than in a control condition. In a prospective dyadic study among newlyweds, we extended these results to close relationships. The results confirmed our hypotheses. Additionally, we found that low trait self-control makes people prone to CIU, illustrating that assessing others’ CIU is a good strategy to gauge others’ level of self-control. These results illuminate how and why CIU may be harmful for relationships.