Equine multinodular pulmonary fibrosis (EMPF) is a progressive fibrosing interstitial lung disease, which has been associated with γ-herpesviruses. This report describes a 22-year-old Warmblood stallion diagnosed with EMPF on the basis of clinical examination, laboratory results, lung radiographs and ultrasound, lung biopsy and inclusion bodies found in macrophages of broncho-alveolar lavage fluid (BALF) as well as an identification of EHV-5 DNA by polymerase chain reaction (PCR). The horse recovered after one week of treatment with valacyclovir (40 mg/kg bwt per os q. 8 h) and is clinically healthy 2 years later. To our knowledge this is the first report describing treatment of EMPF with valacyclovir.