This is an observational study to monitor the continued effectiveness of Ventavis (inhaled iloprost) in the long-term. The study observes the effects and the safety of Ventavis inhalation therapy over at least 2 years and up to 4 years. A total of 54 patients from around 30 study sites in Europe will be included in the study. This observational study will collect information in patients receiving a medication that is already available on prescription in the participating countries. Ventavis is used to treat moderate cases of primary pulmonary hypertension.