Background: For psychiatric service users, the personal social network offers resources such as behavioural guidance, social support, and coherence of care delivery. So far, most research on the subject has assessed the availability of these resources using size and composition measures. However, the availability of network resources also depends on the cohesion of the relationships between network members, a topic that is rarely addressed in the literature. Aims: In this article, we aim to describe the cohesion of psychiatric service users’ networks. Method: We carried out a personal network survey and collected data on the social networks of 380 service users recruited in outpatient and inpatient services in Belgium. We used an ego-network mapping technique. The data were analysed using several structural metrics describing size, composition, and cohesion. We carried out analysis of variance (ANOVA) in relation to residential status, level of education, psychiatric history, and psychosocial functioning and analysed three cohesion indicators (density, fragmentation, and centralisation) with regression analyses. Results: Personal social networks were small and not very cohesive. Most were composed of a dense subgroup as well as several isolated network members. The analyses revealed that highly educated psychiatric service users had more fragmented networks, while users living in independent accommodation had less dense networks. Density and fragmentation were not associated with the severity of psychosocial functioning, whereas centralisation was. Conclusions: The low level of cohesion may indicate that service users aim to access multiple and diverse social resources and that better-off service users are more successful at doing so. On the whole, however, these personal social networks were fragile, because they contained a high number of isolated network members. Finally, it could be beneficial for professionals to pay special attention to the central persons within the networks of psychiatric service users.