Professional social workers am called on to assist many vulnerable cli
ent populations. One such group consists of adults with coexisting sub
stance use and mental disorders who are at risk for HIV infection. Thi
s article presents an evaluation of a social group work intervention d
esigned to help dually disordered adults change sexual behaviors that
increase their risk of HIV infection. Thirty clients attending a day t
reatment program for dually disordered adults agreed to participate in
an AIDS awareness and prevention group. Using a nonequivalent control
group evaluation design, clients were systematically assigned to eith
er the first cycle of the group or to a waiting list. Findings demonst
rated that, compared to persons on the waiting list, clients who recei
ved the preventive intervention improved their understanding of correc
t condom use, used condoms more often, reduced risky sexual practices,
and were more assertive in sexual encounters. Behavioral changes were
attributable to group involvement and not the clients' pregroup chara
cteristics. This was a limited pilot evaluation. The results, however,
should encourage social workers developing AIDS preventive interventi
ons for a particularly vulnerable client population.