Pulmonary hypertension (PH) is a general term that is used to describe high blood pressure in the lungs from any cause. This is a different problem than high blood pressure in the whole body (systemic hypertension). There are five different groups of pulmonary hypertension that are based on the causes. Different types of PH can require different treatment but all forms of pulmonary hypertension are serious and can be life-threatening. Pulmonary hypertension can develop in children or adults at any age. This fact sheet will focus on adults and describe what happens in PH and groups. For more information about pulmonary hypertension in children and the diagnosis and treatment of pulmonary hypertension see the Patient Information Series fact sheets at www.thoracic.org/patients.