BACKGROUND AND OBJECTIVES: Primary (idiopathic) pulmonary hypertension is a rare, progressive and fatal disease. It has been defined, by the World Health Organization, as a mean pulmonary arterial pressure greater than 25 mmHg at rest, or greater than 30 mmHg during exercise, without the apparent cause of secondary pulmonary hypertension. This study was performed to better understanding the clinical presentation, natural history and prognosis of primary pulmonary hypertension. SUBJECTS AND METHODS: A total of 18 patients, who were diagnosed as primary pulmonary hypertension, at three University Hospitals, were retrospectively reviewed. All patients had undergone echocardiography and cardiac catheterization. RESULTS: With the patients there was a male: female ratio of 1:8, ranging in age between 10 and 50 years. The most common presenting symptom was dyspnea on exertion, with other symptoms comprising of fatigue in 11, chest pain in 5, syncope in 3 and hemoptysis in 2. The ECG & echocardiography reflected the presence of right-sided heart enlargement. The average right ventricular systolic pressure, from Doppler echocardiography, was 73.6+/-18.8 mmHg. The mean pulmonary artery pressure and pulmonary capillary wedge pressure were 52.9+/-18.4 and 9.2+/-3.1 mmHg, respectively. The survival times were within 30 and 21 to 60 months in 9 and the remaining patients, respectively. CONCLUSION: We conclude that primary pulmonary hypertension is common in female patients in their third to fifth decades. This study also showed a poor prognosis, as in other reports.