In Vietnam, ARV access has been scaled up since 2005 in high HIV prevalence areas in order to meet increasing demands for HIV treatment. This paper aims to estimate ARV unmet need and its associated socio-demographic characteristics among HIV-positive women in Haiphong, Vietnam. A cross-sectional study using structured questionnaires and CD4 cell count was conducted with 353 HIV-positive women recruited from groups of people living with HIV/AIDS (PLWHA), by snowball technique through member of PLWHA groups and the local AIDS management system (Provincial AIDS Center (PAC)). The percentage of HIV-positive women having an unmet ARV need was estimated to be 40%, particularly high among women who were not registered at PAC. Having an unmet ARV need was associated with not participating in PLWHA groups (OR 6.5; 2.4–17.2) and being younger than 30 years old (OR 2.9; 1.1–7.3).