This study compared two contemporary approaches to linking housing and mental health services. In the integrated housing program, case management and housing services were provided by teams within a single agency and were closely coordinated. In the parallel housing condition, case management services were provided by mobile assertive community treatment teams and housing by routine community-based landlords. Adults with severe mental illness who were at high risk for homelessness (n = 121; 72.7% schizophrenia spectrum) were assigned randomly to integrated or parallel housing services and followed for 18 months. Integrated housing services led to more days of stable housing and greater life satisfaction than parallel housing services, especially for male participants. Integrated housing services were also associated with greater reductions in psychiatric symptoms. Closer integration between clinical and housing services, and greater use of supervised living settings, led to more time in stable housing for participants in the integrated housing services condition and was associated with greater gains in several outcome domains.