A twelve year-old Thoroughbred mare presented with a chief complaint of fever, increased respiratory rate, exercise intolerance and weight loss. On physical exam, the mare was thin, febrile, tachycardic, and harsh lung sounds with crackles and wheezes were auscultated bilaterally. Ultrasonography revealed diffuse pleuritis with multiple small nodules of consolidation. Thoracic radiographs revealed a diffuse interstitial pattern. Tracheal fluid was characterized as suppurative inflammation. A sample of bronchoalveolar lavage tested positive for Equine Herpesvirus 5 (EHV-5) by type specific PCR. The mare was diagnosed with Equine Multinodular Pulmonary Fibrosis (EMPF) and treated with dexamethasone. She continued to deteriorate despite treatment and was euthanized. A necropsy was performed; gross and histologic lung pathology was consistent with the clinical diagnosis of EMPF. EMPF is a recently described disease hypothesized to have an association with EHV-5 infection.