Vietnam s HIV epidemic is concentrated,both in specific behavioral sub-populations and geographicregions. The key populations at higher risk for HIVinfection in Vietnam are female sex workers (FSW) and theirclients; injecting drug users (IDU); and men who have sexwith men (MSM). Vietnam identified harm reductioninterventions for IDU and FSW as a key component of its last5-year National HIV strategy 2004-2009. Harm reductioninterventions aim to reduce the dominant behavioral riskfactors that facilitate transmission of HIV in Vietnam,namely, sharing injecting equipment and engaging inunprotected sex. The main service components of harmreduction for these groups include the distribution of freesterile needle-syringes and condoms and providing behaviorchange communication through peer educator-based outreach.As the next phase of programming is planned and resourcesallocated, it is important to assess the achievements ofprevious programs aimed at minimizing risk of infection interms of coverage and epidemiological impact. This impactassessment study has the following objectives: To examinecoverage of harm reduction interventions in Vietnam amongIDU and FSW (programs targeted for MSM were not examined)from 2004-2009; to understand the HIV transmission dynamicsin Vietnam and to estimate the extent to which harmreduction interventions among core groups have contributedtowards epidemiological trends and reduced HIV transmissionin Vietnam during the 2004-2009 strategy.