In this issue of CHEST (see page 655), Ploegstra and colleagues4 report on clinical worsening of PH in pediatric patients enrolled in a Dutch national registry. As in the SERAPHIN trial, events including death, lung transplantation, PAH-related hospitalization, initiation of IV prostanoids, and functional deterioration (World Health Organization functional class deterioration, a ≥ 15% decrease in 6-min walk distance, or both) were evaluated. In this series of pediatric subjects, the most common event of clinical worsening was functional deterioration. The occurrences of either hospitalization, initiation of IV prostanoids, or functional deterioration were predictive of death or lung transplantation. The authors suggest that clinical worsening may be useful as a study end point in future clinical PAH trials in children.