We examined the ability of a DNA vaccine comprising the Toxoplasma gondii tachyzoite immunodominant surface antigen, SAG-1, to both protect adult BALB/c mice against infection with the avirulent Beverly type-2 strain of T. gondii and also to inhibit the incidence of congenital disease. Vaccination induced an enhanced type-1 immune response as measured by IgG2a antibody production and increased splenocyte IFN-gamma production. Vaccination also limited disease following infection via either the oral or peritoneal routes as measured by mortality, pathology or brain cyst burden. While vaccination with plasmid alone also increased splenocyte IFN-gamma production, this afforded no protection and following infection mortality rates and cyst burden counts were similar in this group to that of non-vaccinated animals. Although, vaccination with SAG-1 DNA did protect against adult acquired T. gondii infection, it did not prevent maternofoetal transmission in previously vaccinated dams infected during pregnancy. The results indicate differences in the protective mechanisms operating between adult acquired disease and congenital transmission and have significant implications for future vaccine development.