Twenty-four patients (9M and 15F, mean age 28 years) with primary pulmonary hypertension underwent cardiac catheterization in our institution from 1955 to 1989. The prevalence of the disease in our population was lower (0.2%) than that reported by other Authors (1%). Thirteen of these patients (4 M and 9 F, mean age 32 years) evaluated between January 1979 and December 1989, were followed. Five were alive after 52 +/- 30 months (Group A) while 8 died after 11 +/- 9 months (Group B). In Group B mean pulmonary pressure was significantly higher than in Group A (66.7 +/- 17.2 vs 41.2 +/- 19.0 mmHg, p less than 0.05, respectively). Cardiac index and systolic volume index were lower in Group B than in Group A (2.07 +/- 0.85 vs 3.72 +/- 1.32 l/min/m2, p less than 0.01 and 24.43 +/- 10.25 vs 41.08 +/- 16.97 ml/m2, p less than 0.05, respectively). Pulmonary resistance index and systemic resistance index were higher in Group B than in Group A (3039 +/- 1519 vs 1181 +/- 1236 dyne x s x cm-5/m2, p less than 0.01; 4277 +/- 1794 vs 2309 +/- 1238 dyne x s x cm-5/m2, p less than 0.01). One patient underwent repeated cardiac catheterization after 2 years. This patient showed a deterioration of the hemodynamic parameters, consistent with the worsening of the clinical conditions. In conclusion, in our population of patients with primary pulmonary hypertension, an increase in pulmonary artery pressure and pulmonary resistances, as well as a decrease in cardiac index, are associated with a reduced life expectancy. On the other hand, right atrial pressure does not affect mortality.