The incidence of childhood immersion injury in a defined population is reported. The data were drawn from this Hospital's Child Injury Surveillance programme and cover the period July 1, 1984 to June 30, 1985. The overall rate of immersion injury was 26.8 per year per 100 000 children at risk and the rate for fresh-water immersions was 25.3. The magnitude of this public health problem is revealed by an annual fresh-water immersion rate of 70.2 per 100 000 at risk for the critical 0 to four years' age group. Eighty per cent of all immersions occurred in swimming-pools and the rate of pool immersion is three times that reported in the Brisbane Drowning Study (1971-1975). Eighty per cent of immersions in back yard pools were potentially avoidable by the provision of an effective safety barrier. Only 25% of the families that were involved could be described as being familiar with their pool.