BACKGROUND: Brief face-to-face-behavioral interventions have been shown to be efficacious, but are costly to sustain and to widely disseminate. This study evaluated the efficacy of a 15-minute theory-based behavioral intervention designed to increase condom use and reduce new cases of Neisseria gonorrhoeae and Chlamydia trachomatis. METHODS: Participants were randomly assigned via the computer to the intervention or the comparison group stratified by gender and their baseline stage of change (motivational readiness) for using condoms consistently (100%) with their main partners. Behavioral data and biologic specimens for testing of Neisseria gonorrhoeae and Chlamydia trachomatis were obtained at baseline and at 6 months post intervention. The intervention was delivered via an audio, multimedia, computerized application that provided individualized interventions to patients based on their responses to assessment items; comparison patients interacted with a 15-minute, computerized, multiple health risk assessment with no intervention. RESULTS: The majority of the sample (N = 430) was black (88%); 54.5% women; with a mean age = 24.5. Assuming all participants who did not return to the clinic at 6 months were not using condoms consistently, 32% of the treatment group versus 23% in the comparison group reported consistent condom use (P = 0.03). The combined Neisseria gonorrhoeae and Chlamydia trachomatis incidence declined to 6% in the intervention group versus 13% in the comparison group (P = 0.04). Results from a regression analysis revealed that the only statically significant predictor of sexually transmitted diseases infection at the follow-up was group assignment (OR = 1.91, 95% confidence index = 1.09-3.34; P = 0.043). CONCLUSIONS: These findings suggest that brief, interactive, computer-delivered interventions provided at the evaluation visit increase condom use and reduce sexually transmitted diseases without putting additional burden on clinicians or staff. © 2009, American Sexually Transmitted Diseases Association.