Toxoplasmosis is a neglected disease in Vietnam particularly in populations with a high risk of developing complications. The seroprevalence of Toxoplasma gondii was calculated by testing blood samples for Toxoplasma specifically immunoglobulin G and immunoglobulin M on 300 intravascular drug users and on 300 pregnant women. Among intravascular drug users, the seroprevalence of IgG and IgM was 7.7% and 0.08%, respectively. In pregnant women the prevalence of anti-toxoplasmosis IgG and IgM was respectively 11.2% and 0%. 0.28% of all estimated pregnancies in Vietnam are affected with toxoplasmosis, i.e. around 4800 pregnancies per year. In conclusion, a screening of Toxoplasma infections should be recommended in HIV/AIDS patients.