Phrenic nerve palsy (PNP) is seen in infants and young children usually resulting from operative trauma or birth injury. Spontaneous recovery usually occurs, but occasionally surgical plication is necessary. Twenty-three cases of PNP over a 10-year period were managed surgically. Patient ages ranged from 1 day to 30 months (median, 4 months), 18 were male and five female. Cause was operative trauma in 18 (17 cardiac surgery, one neuroblastoma), birth trauma in two, and idiopathic in three. The right side was involved in 14, the left in eight, and both in one. Indications for plication were inability to wean from the ventilator (group 1, 16 patients), recurrent pneumonia (group 2, four patients), and respiratory distress (group 3, three patients). The 16 patients in group 1 were intubated for a median of 18.5 days from onset of PNP to plication. Postoperatively, three had continuing congestive heart failure (one died at 16 days of age, one was still chronically ventilated at 22 months, one was extubated at nine days); the other 13 were extubated at a median of two days postoperatively. All the patients in groups 2 and 3 were extubated within two days of surgery. Twelve plications were transthoracic and 11 were transabdominal. Postoperative complications included pneumonia (2), wound infection (1), pneumothorax (2), and mucous plug with pulmonary collapse (1). One patient died of cardiac failure at 16 days. One patient in group 3 developed recurrent respiratory distress 4 months postoperatively; he had a recurrent elevated hemidiaphragm requiring a second plication.(ABSTRACT TRUNCATED AT 250 WORDS)