Objectives This study aimed to determine the seroprevalence of Toxoplasma gondii (T. gondii) infection in pregnant women in Matehuala City, Mexico; and the associated risk factors.Design A cross-sectional study.Setting Matehuala City, Mexico.Participants 311 pregnant women.Primary and secondary outcome measures Sera of women were analysed for anti-T. gondii IgG and IgM antibodies by commercially available immunoassays. Bivariate and multivariate analyses were used to assess the association between T. gondii seroprevalence and the characteristics of the pregnant women.Results Thirteen (4.2%) of the 311 pregnant women studied were positive for anti-T. gondii IgG antibodies. No anti-T. gondii IgM antibodies were found in anti-T. gondii IgG seropositive women. No association between seropositivity and history of blood transfusion, transplantation, caesarean sections, deliveries, miscarriages or number of pregnancies was found. Logistic regression analysis of sociodemographic, behavioural and housing variables showed that availability of potable water at street represented a risk factor for T. gondii infection (age-adjusted OR=2.18; 95% CI: 1.05 to 4.53; p=0.03), whereas being born in Mexico was a protective factor for infection (age-adjusted OR=0.01; 95% CI: 0.001 to 0.35; p=0.008).Conclusions In this first study on the seroepidemiology of T. gondii infection in pregnant women in Matehuala, we conclude that the seroprevalence of T. gondii infection is low and similar to those reported in pregnant women in other Mexican cities. However, the seroprevalence found is lower than those reported in pregnant women in other countries in the Americas and Europe. Two risk factors associated with T. gondii infection were identified. Results of the present study may help for the optimal planning of preventive measures against toxoplasmosis in pregnant women.