Drowning is a common cause of injury death for children. Medical care for drowning victims does little to increase the chance of survival with good neurological recovery. Prevention efforts to date have included pool fencing, use of personal flotation devices, and promotion of swimming lessons for older children. This case-control study sought to examine the association of swimming lessons and risk of drowning in children aged 1 to 19 years. Of the 61 drowning cases in 1- to 4-year-olds, only 3% had participated in formal swimming lessons compared with 26% of matched controls. Swimming lessons for these younger children were associated with an 88% lower risk of drowning. Among those aged 5 to 19 years, swimming lessons were associated with a 64% lower risk of drowning, though this difference was not statistically significant. Formal swimming lessons may have the potential to make dramatic reductions in the risk of drowning in preschool-aged children.