Objectives: This study estimated the effects of local pool-fencing ordinances and other factors on the rate of childhood drowning in Los Angeles County, California. Methods: Stage 1 was a retrospective dynamic cohort study of all drownings among children younger than 10 years that occurred in residential swimming pools in Los Angeles County between 1990 and 1995. Stage 2 was a matched case-control study that compared pools in which childhood drownings occurred (cases) with randomly selected pools in which drownings did not occur (controls). Results: The drowning rate was relatively high among toddlers (aged 1-4 years), boys, and African Americans and in areas with a high density of residential swimming pools. Pool-fencing ordinances were not associated with a reduced overall rate of childhood drowning. Conclusions: Local ordinances enacted in Los Angeles County before 1996 do not appear to have been effective in reducing the rate of childhood drowning in residential pools. Possible reasons for this ineffectiveness are insufficient building codes for isolating pools from homes, inadequate enforcement of the ordinances, and inadequate operation or maintenance of fencing equipment by pool owners.