The investigation was designed to explore correlations and causal links between the social networks and social support of the cohort and violence they committed toward others during an 18-month period. Study subjects were 169 persons with severe, persistent mental illnesses, who were recruited from four hospitals. Six interviews were conducted with the subjects over a 32-month period. Significant others or family members were interviewed once separately. The analysis reported in this chapter covers the first 18 months of the study period. Medical records were reviewed, as were arrest records from courts in the five counties of residence of study participants. A violent act was defined as an arrest or criminal charge and adjudication for assault and battery, manslaughter, or murder; a danger-to-others commitment that specified that the respondent hit, hit with an object or weapon, sexually assaulted, or threatened with an object or weapon another person; or a confirmed report of a violent act by the respondent. The findings show that approximately one-third of the cohort of people with major mental illnesses engaged in behaviors that were actually or potentially dangerous to others during an 18-month period. Nearly twice as many threats were made than acts committed, and very few individuals were arrested for or charged with violent crimes. Social and demographic characteristics were not significant predictors of violent acts and only slightly salient in predicting violent threats. Clinical variables proved to be the only significant predictors of who would engage in violent acts, and violent threats were influenced in various ways by the social, clinical, previous violence, and social network and support characteristics of the cohort. Individuals with a diagnosis of schizophrenia were substantially more likely than others to commit acts of violence toward others, but no more likely to threaten others than people with other diagnoses. Further, the findings support the guiding presumptions, that is, that the structure and nature of an individual's relations with others, in combination with their subjective experiences, clinical condition, and personal histories, provide some indication of who will be violent toward whom. 5 tables, 1 figure, and 55 references