OBJECTIVES: To evaluate treatment patterns and healthcare costs associated in patients initially treated with PDE-5i monotherapy for pulmonary hypertension(PH). METHODS: Patients ages ≥18 with ≥2 diagnostic claims for PH (ICD-9 416.0 or 416.8) and ≥1 claim for any PDE-5i (index date) between 1/1/2009 and 12/31/2013 were selected from PharMetrics Plus, a U.S. claims database. Continuous enrollment ≥6 months before and ≥12 months after index were required, as well as a PH diagnosis prior to index. Patients with combination PH therapy, with endothelin receptor antagonist or prostacyclin analogue, or PDE-5i brands for erectile dysfunction were excluded. Time to treatment modification was defined as days between first PDE-5i prescription and discontinuation, augmentation or medication switch, and was measured via Kaplan-Meier survival analysis and a multivariable Cox Proportional Hazards model. Direct medical costs in the one year following index were inflated to 2014 dollars.  RESULTS: A total of 1,465 PH patients (405 tadalafil, 1,060 sildenafil) had an index claim for PDE-5i.  At 365 days post-index, 66% of tadalafil patients remained without treatment modification, compared to 56% of sildenafil patients (p<0.001).  In the adjusted Cox model, tadalafil showed significantly lower risk of treatment modification in one year compared with sildenafil [HR=0.75 (95% CI 0.62-0.92), p=0.005]. The mean (SD) total all-cause cost per patient was $120,369 ($189,365) [inpatient $47,146 ($155,302), outpatient $40,886 ($81,802), and pharmacy $32,337 ($34,228)]. At least one hospitalization was experienced in 44.4% of the patients; their cost was $197,111 ($251,651) compared to $59,164 ($74,488) in patients with no hospitalization. CONCLUSIONS: PH patients treated with PDE-5i monotherapy had a substantial risk of treatment modification and hospitalization within one year of starting therapy, resulting in increased healthcare costs.  These outcomes may indicate disease progression and highlight the need to achieve established treatment goals outlined in the 2015 ESC/ERS PH Guidelines.