This study examined the effects of integrating mental health, substanc
e abuse, and housing interventions for homeless persons with co-occurr
ing severe mental illness and substance use disorder. With the use of
a quasi-experimental design, integrated treatment was compared with st
andard treatment for 217 homeless, dually diagnosed adults over an 18-
month period. The integrated treatment group had fewer institutional d
ays and more days in stable housing, made more progress toward recover
y from substance abuse, and showed greater improvement of alcohol use
disorders than the standard treatment group. Abuse of drugs other than
alcohol (primarily cocaine) improved similarly for both groups. Secon
dary outcomes, such as psychiatric symptoms, functional status, and qu
ality of life, also improved for both groups, with minimal group diffe
rences favoring integrated treatment.