Eighteen children sustained unilateral phrenic nerve paralysis (PNP) after cardiac surgical procedures. Ten (Group I), under 7 months (mean: 2.9 +/- 2.2), required long-term ventilatory assistance (mean: 23.9 +/- 13.0 days); they failed to be weaned from the ventilator. All underwent diaphragmatic plication (DP). DP was performed late in 7 cases (Group Ia) with a mean time of 30.8 days between surgery and DP, and early in 3 others (Group Ib) with a mean time of 10.2 days. Eight children (Group II), older than 1 year, tolerated PNP better and could be extubated early without diaphragmatic plication. In Group Ia severe lung infections were recorded in 5 before or/and after DP, and two died at 3 and 30 days after plication. Five children from Group Ia and all 3 from Group Ib were late survivors. They could be weaned from ventilatory support in a mean time of 3 days after DP, although those with severe lung infection (Group Ia) took the longest time. All from Group II were late survivors. We conclude: PNP is well tolerated without plication in children older than 1 year. However early DP offers excellent and immediate results in infants with PNP. Early DP in these children avoids or reduces severe lung infections and death.