A case-control study of 305 children was done to evaluate the relationship between toxocariasis and seizures and risk factors associated with toxocariasis transmission and seizure onset. A significant association existed between seropositivity for anti-Toxocara canis and seizures (p less than 0.05); the correlation was closest in children aged less than 5 years of age. Among risk factors, pica was more common in children with seizures than in controls but was not associated with toxocariasis. The association between dog ownership and toxocariasis was highly significant (p less than .000001). Our findings suggest that toxocariasis may be involved as a cofactor in the pathogenesis of seizures.