Recent research has greatly improved our understanding of the pathophysiology of pulmonary hypertension. There is increasing recognition that pulmonary hypertension is an important complication of many childhood respiratory diseases including cystic fibrosis, interstitial lung diseases, upper airways obstruction and disorders of the respiratory muscles and chest wall. Chronic hypoxaemia and, in some cases, destruction of the vascular bed are the key factors. The clinical features of pulmonary hypertension are often overshadowed by those of the primary respiratory disease but newer imaging techniques allow earlier detection of this complication. This may be important in the future if new specific therapies for primary pulmonary hypertension are shown to be beneficial in secondary pulmonary hypertension. With some conditions, such as airways obstruction due to adenotonsillar hypertrophy, treating the underlying cause leads to rapid resolution of the hypertension. However, with most disorders, such as cystic fibrosis, management is focused on treating the lung disease intensively and correcting the chronic hypoxaemia with oxygen therapy, sometimes augmented by nasal mask ventilation. However, although several new selective therapies are effective in idiopathic pulmonary arterial hypertension, their role in secondary pulmonary hypertension remains unclear.