CASE PRESENTATION: A 52-year-old female ex-smoker was diagnosed with ulcerative colitis (UC) in 2013. Dyspnea began in 2014 and was presumed due to emphysema. She did not respond to inhalers. UC was poorly controlled with adalimumab (previously 5-ASA and 6-MP). Exam was notable for hypoxia. PFTs showed severe obstruction and air trapping (FEV1 27% predicted, FVC 53%, ratio 51%, DLCO 61%, RV 167%). CTA chest did not show emphysema or VTE but suggested OB. Surgical lung biopsy confirmed this and showed thick-walled pulmonary arteries with thrombus in two lobes. V/Q scan and venous Doppler ultrasound were negative. Echocardiogram was negative for pulmonary hypertension. Oral steroids were started. Symptoms improved, diffusing capacity normalized, and oxygen requirements resolved. Steroid taper initially failed. Infliximab was started with improvement to both UC and pulmonary symptoms, now nearly off steroids with continued improvement.