To determine epidemiological and clinical associations with Toxocara canis seropositivity, we studied 333 (87%) children of a cohort of 383 five- to seven-year-olds. The prevalence of seropositivity (antibody titer to T canis, greater than or equal to 1:32) was 23.1%. Black children were more frequently seropositive than were white children, as were children of parents who did not graduate from high school. In a sample of seropositive and seronegative children, seropositivity was associated with both a history of pica and puppy ownership, but not with a greater frequency of symptoms and signs that occur in visceral larva migrans or with poor growth. No child had evidence of ocular toxocariasis on retinal examination. For the whole sample, poor reading achievement, marked distractibility, and lower intelligence were associated with seropositivity, but by using multiple regression analysis, we found that these associations may be attributable to confounding variables.