To assess rubella and measles susceptibility among women of childbearing age we conducted a cross-sectional seroprevalence study in four cities and one rural area in Argentina. A convenience sample of women aged 15–49 years seeking care in public health-care institutions was selected (n=2804). Serum specimens were tested for rubella and measles IgG antibody titres. The overall susceptibility to rubella and measles was 8·8 and 12·5% respectively. Seroprevalence differences were found for both rubella (P<0·001) and measles (P=0·002) across sites. Rubella seroprevalence was higher in women aged [ges ]40 years than in younger women (P=0·04). Measles seroprevalence tended to increase with age (P<0·001). Approximately 15% of women aged 15–29 years were not immune to measles. No risk factors were associated with rubella seronegativity; however, age (P<0·001) and having less than four pregnancies (P<0·001) were factors associated with measles seronegativity. Our findings support the introduction of supplemental immunization activities targeting adolescents and young adults to prevent congenital rubella syndrome and measles outbreaks over time.