Percutaneous balloon dilatation of a Waterston anastomosis was performed in a child who had had four shunt operations. Initially, the procedure was apparently successful, but pulmonary oedema developed and he died 12 hours after the procedure. Balloon dilatation of a Waterston anastomosis is technically possible and may prove to be an alternative to reoperation in certain patients. But further experience with the technique is necessary to determine the optimum size of the inflated balloon, and to avoid the risk of producing an excessive increase in pulmonary blood supply.