We evaluate the influence of housing, services, and individual characteristics on housing loss among formerly homeless mentally ill persons who participated in a five-site (4-city) study in the U.S. Housing and service availability were manipulated within randomized experimental designs and substance abuse and other covariates were measured with a common protocol. Findings indicate that housing availability was the primary predictor of subsequent ability to avoid homelessness, while enhanced services reduced the risk of homelessness if housing was also available. Substance abuse increased the risk of housing loss in some conditions in some projects, but specific findings differed between projects and with respect to time spent in shelters and on the streets. We identify implications for research on homeless persons with mental illness that spans different national and local contexts and involves diverse ethnic groups.