The delivery of HIV risk assessment and behavioral counseling by clinicians in HIV clinical settings is one component in a comprehensive "positive prevention" strategy to help patients reduce their transmission risk behavior. Clinicians engage in behavioral prevention inconsistently, however, depending on whether patients are new to a practice or are established in regular care and on their attitudes and characteristics of their practices. We analyzed clinician reports of behavioral prevention delivered before and after participation in a large federal demonstration project of positive prevention interventions. The interventions that were part of this project were successful in increasing behavioral prevention among both new and returning patients. Prior to study interventions, clinicians reported counseling 69% of new patients and 52% of returning patients. In follow-up interviews 12 months after receiving training, clinicians reported delivering prevention messages to 5% more new patients and 9% of returning patients (both p<0.01). After 12 months, clinicians were more likely to engage in behavioral prevention if other providers in their sites were also involved. Clinicians agreeing that behavioral prevention was part of the clinic's mission were more likely to conduct it. The interventions were successful in mitigating the influence of provider attitudes precluding prevention delivery. Intervention strategies can help clinicians more consistently deliver behavioral prevention messages to their HIV-infected patients.