Since 1978, 136 preterm babies received ligation of a patent ductus arteriosus as day cases. A total of 122 babies whose notes were available for review, with a median gestational age of 27 weeks (range 23-35) and median birth weight of 960 g (range 470-2750), were transported distances of up to 80 miles. The median ages at ligation with and without previous medical management with indomethacin were 23 and 15 days, respectively. One hundred and ten (90%) babies were dependent on ventilatory support, but extubation was achieved at a median time of 10 days after ligation, regardless of postnatal age at the time of ligation. There were no deaths associated with the operation, and no complications resulting from transportation. The hospital mortality was 15 (12.3%), and the most important (and significant) adverse factor was a preoperative fractional inspiratory oxygen content greater than 0 3. The results of this study show that day case ligation of the patent ductus arteriosus is safe, and if it is carried out early will reduce the time before extubation and discharge from the intensive care unit.