Numerous experimental studies have shown several benefits of treating burns by the immediate application of cool water. In this study of 695 children with burns, treated in the National Burn Institute (NBI), Hanoi, Vietnam, patients were assessed on admission according to first aid measures at the time of injury, i.e. the removal of the cause and immediate cooling with cold water. A total of 33% of the children who had had immediate cooling of the burn with water had deep burns, compared with 49% of the children who had not had immediate cooling. The prevalence ratio of deep burns was thus 0.68 (95% confidence interval (CI) 0.55-0.85); that is, there was an estimated reduction of 32% in the need for skin grafting, a reduction which was statistically significant. After adjusting for the effect of cooling the burn, removal of the causal agent reduced the odds of requiring skin grafting, but the reduction was not statistically significant. It is concluded that early cooling will prevent a significant percentage of superficial burns from progressing to deep burns. This will not only reduce the probability that skin grafting and expensive treatment will be required, but will reduce the risk of other consequences of deep burns, which may be fatal. Public health programs to promote immediate cooling of burns with cool water are at least as important as subsequent medical and surgical treatment in determining the outcome of burns in children.