Vietnam's HIV epidemic is driven by injection drug use. Most IDUs are sexually active and may infect their female sexual partners (SPs). We implemented peer-based HIV prevention interventions for SPs in Hanoi. This paper reports on an evaluation of these interventions based on cross-sectional surveys of SPs. Our data show that this population can be reached, relationships improved, and consistent condom use increased (27% at 24 months up from 16% at 12 months: P = 0.002). Self-reported condom use at last sex was 3.5 times higher among participants in the intervention than among non-participants after controlling for selection bias, indicating a possible intervention effect. However, no significant association was found for consistent condom use in the previous 6 months. Many SPs remain at risk for HIV and interventions must promote a range of HIV prevention strategies including consistent condom use, lower risk sexual activity, and ARV treatment as prevention.