OBJECTIVES: Healthcare cost data for pulmonary arterial hypertension (PAH) are scarce, especially for important morbidity events like hospitalizations, owing to the absence of a unique ICD-9-CM code. This study assessed inpatient costs and length of stay (LOS) among US patients with PAH. METHODS: A retrospective analysis was performed using data (January 2007–December 2011) from adult enrollees with Commercial or Medicare Advantage with prescription drug coverage from a large health plan. PAH patients were identified based on both ≥1 medical claim with an ICD-9-CM code for primary pulmonary hypertension (PH) (416.0) or other chronic pulmonary heart disease (416.8), and ≥1 pharmacy claim for a medication indicated for PAH or frequently used in PAH. Patients had to have ≥365 days of enrollment prior to index date (study inclusion) and 180 days during follow-up. Discharge diagnoses being unavailable, the principal diagnosis for each hospitalization was defined as the most frequent primary diagnosis on that hospitalization's facility claims. Total hospitalization costs (inflated to 2011 USD using the CPI-U) and LOS, stratified by payer (excluding dual eligibility) and principal diagnosis, were analyzed with descriptive statistics. RESULTS: The 4009 PAH patients (52% female, mean±SD age 60±14 years) incurred 5582 hospitalizations. Hospitalization cost was $34,123±107,005 (mean±SD), and was nearly 3 times higher for hospitalizations with Commercial ($46,118±135,137, n=3322) than Medicare Advantage coverage ($16,319±30,046, n=2244). Average cost was higher for hospitalizations with a principal diagnosis of PH (416.0 or 418.6) than other principal diagnoses ($49,722±181,878, n=878 vs $31,211± 85,821, n=4704). Average LOS was 11.7±20.8 days, and was longer for hospitalizations with Medicare than Commercial coverage (12.8±21.2 vs 10.9±20.4 days), and for hospitalizations with PH as principal diagnosis compared with other principal diagnoses (15.0±30.5 vs 11.1±18.3 days). CONCLUSIONS: Long durations and high incurred costs for PH-related hospitalizations reveal the severe morbidity, healthcare, and patient burden of PAH.