CASE PRESENTATION: A 45-year-old woman with neurofibromatosis presented with a 4 year history of worsening exertional dyspnea equivalent to WHO functional class (FC) IV. Chest CT prior to evaluation ruled out pulmonary embolism but showed diffuse bilateral ground-glass infiltrates and a prominent main pulmonary artery (PA) measuring 4cm. She had been given the presumptive diagnosis of interstitial pulmonary fibrosis but had not improved on steroids. Arterial blood gas confirmed hypoxemia on room air with PaO2 56mmHg. Pulmonary function testing showed mild restriction with total lung capacity 74% and diffusing capacity 52% predicted. Repeat chest CT revealed low lung volumes, mild centrilobular emphysema, and marked enlargement of the main PA (4.4cm) but no diffuse interstitial lung disease. Echocardiography showed moderate right atrial and severe right ventricular (RV) enlargement, and severe decrease in RV systolic function. Right heart catheterization (RHC) demonstrated right atrial pressure (RAP) 20mmHg, mean PA pressure (MPAP) 54mmHg, pulmonary capillary wedge pressure 9mmHg and cardiac output (CO) 1.6L/min. The calculated PVR was greater than 28 Woods units. There was no step-up in O2 saturation or significant response to inhaled nitric oxide. Due to financial limitations, patient was reluctant to initiate infusion prostanoid therapy; therefore, sildenafil and bosentan were started. Six month follow-up showed persistently elevated brain natriuretic peptide level and reduced 6 minute walk distance with severe RV enlargement and dysfunction by echocardiography. The patient was admitted for RHC and initiation of continuous epoprostenol infusion, which offered significant improvement in MPAP, CO and PVR on 10ng/kg/min epoprostenol: MPAP decreased from 75 to 49mmHg, CO increased from 5 to 9L/min and RAP decreased from 24 to 18mmHg. Upon follow-up, patient was switched from sildenafil to tadalafil. When she developed pancytopenia from myelodysplastic syndrome, bosentan was discontinued. Currently, she is FC II on epoprostenol 50ng/kg/min and tadalafil 40mg daily.