The paucity of data on the natural history of primary pulmonary hypertension (PPH), and the observation that some patients awaiting heart-lung transplantation (HLT) appeared to be living longer than expected, led us to analyze the survival data of patients with PPH who had been referred for consideration of HLT. Ninety patients (female: male = 3.6:1) met clinical and hemodynamic criteria for PPH. Age at diagnosis was 29.8 +/- 7.9 years (mean +/- SD) (range 13-48 years). Symptom duration was 65.9 +/- 47.4 months, while survival from diagnosis was 42.9 +/- 42.6 months, giving a mean lead time of 23 months. Mean pulmonary artery pressure (PAP) at diagnosis was 61.6 +/- 15.0 mm Hg. The incidence of patent foramen ovale (PFO) was 19 percent, postpartum onset 16 percent, family history 6 percent, and cirrhosis 3 percent. The survival of 27 patients who died without operation was 50.3 +/- 52.5 months (median 37 months), with a symptom duration of 68.4 +/- 57.5 months (median 64 months). Both a high mean right atrial pressure (RAP) (p less than 0.025) and high mean PAP (p less than 0.025) correlated inversely with survival. For the whole group, none of the variables, age at diagnosis, sex, mean PAP or mean RAP at diagnosis, symptom duration prior to diagnosis or the presence of a PFO, postpartum onset or positive family history, significantly influenced survival. However, a low cardiac output (p less than 0.05) adversely influenced prognosis. The discrepancy between the mean and median length of survival in our group and previous reports confirms the need for further clarification of natural history and for appropriate clinical trials to assess therapeutic endeavors.