This study explores three social network characteristics as they relate to demographic, clinical, and quality of life factors. The sample consists of 219 participants with serious mental illness. Results indicate that clients' social networks were small, and that network size is robustly related to symptoms and other measures of clinical and cognitive functioning, as well as with quality of life and self-esteem. The expected relation between network density and either the demographic variables or quality of life was not found. Moderate levels of network density, however, were associated with fewer psychiatric symptoms and higher IQ. Network multiplexity was most highly associated with demographic variables, such as ethnic minority status, less education, never being married, and living with family.