Objective: Social support for patients with a mental illness has been associated with a lower rate of hospitalization. It is important to clarify the role played by a lack of social support as a possible predictor of emergency compulsory admission. Methods: A random sample of 252 patients who were evaluated by two psychiatric emergency teams in Amsterdam from September 2004 to September 2006 were interviewed approximately one month later about their social networks and social interactions. The number of emergency compulsory admissions was recorded for 244 patients during a two-year follow-up period after the interviews. Results: Patients who lived alone had a higher risk of compulsory admission (p≤.05) and had fewer people in their social network (4.6 versus 6.1, p≤.001) compared with patients who lived with others. Among patients who lived alone, the percentage of patients with a compulsory admission was significantly higher among the patients with a high score for negative interactions than among patients with a low score (34% versus 13%, p≤.05). Conclusions: Of the social support variables, living alone proved to be the only predictor of emergency compulsory admission and readmission, and patients who lived alone had a smaller social network. A high level of negative social interactions increased the risk of compulsory admission among patients who lived alone.