BACKGROUND Two studies based on clinical samples have found an association between Toxoplasma gondii infection and history of suicide attempt. To our knowledge, these findings have never been replicated in a prospective cohort study. OBJECTIVE To examine whether T gondii–infected mothers have an increased risk of self-directed violence, violent suicide attempts, and suicide and whether the risk depends on the level of T gondii IgG antibodies. METHODS Register-based prospective cohort study. Women were followed up from the date of delivery, 1992 to 1995 until 2006. METHODS Denmark. METHODS A cohort of 45 788 women born in Denmark whose level of Toxoplasma-specific IgG antibodies was measured in connection with child birth between 1992 and 1995. METHODS Incidence rates of self-directed violence, violent suicide attempts, and suicide in relation to T gondii seropositivity and serointensity. RESULTS T gondii–infected mothers had a relative risk of self-directed violence of 1.53 (95% CI, 1.27-1.85) compared with noninfected mothers, and the risk seemed to increase with increasing IgG antibody level. For violent suicide attempts, the relative risk was 1.81 (95% CI, 1.13-2.84) and for suicide, 2.05 (95% CI, 0.78-5.20). A similar association was found for repetition of self-directed violence, with a relative risk of 1.54 (95% CI, 0.98-2.39). CONCLUSIONS Women with a T gondii infection have an increased risk of self-directed violence.