HIV counseling with testing has been part of HIV prevention in the U.S. since the 1980s. Despite the long-standing history of HIV testing with prevention counseling, the CDC released HIV testing recommendations for health care settings contesting benefits of prevention counseling with testing in reducing sexual risk behaviors among HIV-negatives in 2006. Efficacy of brief HIV risk-reduction counseling (RRC) in decreasing sexual risk among subgroups of substance use treatment clients was examined using multi-site RCT data. Interaction tests between RRC and subgroups were performed; multivariable regression evaluated the relationship between RRC (with rapid testing) and sex risk. Subgroups were defined by demographics, risk type and level, attitudes/perceptions, and behavioral history. There was an effect (p < .0028) of counseling on number of sex partners among some subgroups. Certain subgroups may benefit from HIV RRC; this should be examined in studies with larger sample sizes, designed to assess the specific subgroup(s).