Screening of 153 Hispanic children attending a Hospital-based primary care clinic revealed a 16 percent prevalence of Toxocara canis infection. Infections were found in other household occupants for half of these children. Follow-up of 20 children (for periods of up to 7 years) with asymptomatic T. canis infection failed to demonstrate any clinical sequelae. However, longer periods would be necessary to entirely discount the possibility of latent ocular disease. Treatment with thiabendazole did not appear to alter the course of the infection in a controlled 1-year evaluation as measured by eosinophil counts and specific T. canis antibody titers.