Unilateral diaphragmatic paralysis (UDP) is not an uncommon occurrence after cardiovascular operations. Its incidence in the pediatric age group is at least 1.5%, and severely symptomatic (for example: requiring mechanical ventilation) patients account for about one third of the cases. We have encountered four such cases among 850 children (0.5%) undergoing cardiovascular procedures, and have treated two additional patients. All required prolonged intubation and mechanical ventilation. Diaphragmatic plication in five was performed rather late in the course of their illness, after 21-120 days mechanical ventilation, and was successful in three who survived, allowing weaning from ventilation within 3-6 days. The procedure itself is simple and safe. We recommend that diaphragmatic plication be performed early in children with UDP and weaning difficulties.