Primary pulmonary hypertension, although less frequent than secondary forms, represents the true paradigm of this disease. The recent investigations on pulmonary vascular response mechanisms to different stimuli has increased our knowledge about the mechanism of high pulmonary pressure. Molecular biology of the endothelial cell has provided evidence that endothelial injury plus a genetic individual predisposition may be the pathogenic mainstream of this disease. The histologic findings of pulmonary hypertension are still a matter of controversy, although the clinical, epidemiological and prognostic features are better defined. Therapeutically, there has been important advances, specially with various vasodilators, like calciumantagonists, prostacyclin, adenosine and nitric oxide, as well as new routes of administration. In more advance stages of the disease, atrial septostomy (only paliative) and pulmonary or cardio-pulmonary transplantation, are other therapeutic options to consider, after an adequate selection of patients.