INTRODUCTION: Ulcerative colitis (UC) is an inflammatory bowel disorder (IBD) resulting in continuous mucosal inflammation from the rectum with variable extension to the proximal colon. Symptoms can include abdominal pain, hematochezia, or tenesmus. Anti-tumor necrosis factor (anti-TNF) therapy has been recognized as a treatment modality for moderate to severe UC. Extraintestinal manifestations of IBD have been well documented, with pulmonary manifestations being an uncommon presentation. One such manifestation is cryptogenic organizing pneumonia (COP). The most common finding is diffuse ground glass opacities and bilateral infiltrates on CT. In addition, COP has been described as a noninfectious complication associated with anti-TNF therapy. Here we present a case of COP in a patient being treated with an anti-TNF biosimilar for moderate to severe UC. CASE DESCRIPTION/METHODS: A 38 year-old female with left-sided UC presented to the hospital complaining of 2 weeks of progressively worsening shortness of breath. She had been on Inflectra and mesalamine for 2 years without complications. A chest CT revealed bilateral infiltrates concerning for organizing pneumonia. Bronchoscopy with bronchoalveolar lavage (BAL) was negative for fungal, pneumocystis jirovecii, bacterial, or viral etiologies. The patient was eventually discharged, however, she still required supplemental oxygen. She was started on prednisone and Bactrim for pneumocystis pneumonia prophylaxis. She was referred to gastroenterology for a concern of a possible association between Inflectra and COP. Mesalamine and Inflectra were stopped and the patient developed fecal urgency and rectal bleeding. The patient was started on vedolizumab and prednisone with an eventual prednisone taper, in addition to levalbuterol for her ongoing dyspnea. After two months of vedolizumab therapy, the patient noted significant improvement in her gastrointestinal symptoms as well as her pulmonary symptoms. DISCUSSION: There have been case reports detailing COP in patients undergoing therapy with Infliximab, however, this is the first known case of COP with a biosimilar. The improvement in pulmonary symptoms with discontinuing Inflectra, which was controlling her UC, and starting vedolizumab to continue control of the UC with subsequent improvement in her COP suggests the biosimilar, Inflectra, as opposed to an extra intestinal manifestation of UC, was the cause of COP.