Equine multinodular pulmonary fibrosis (EMPF) and primary leukaemia are uncommon diseases in horses. This case report describes a horse with both diseases which might be linked via the equine γ-herpesvirus EHV-5. In man Epstein Barr Virus (EBV), also a γ-herpesvirus, is associated with idiopathic pulmonary fibrosis as is EHV-5 with EMPF. Furthermore, EBV is also associated with lymphoproliferative disease. Similarly in horses, primary leukaemia might be associated with EHV-5. This is the first report associating EHV-5 with primary leukaemia in horses.