Bovine viral diarrhea virus (BVDV) is a ubiquitous virus that is the most frequently isolated viral pathogen of cattle in some areas. BVDV virus infection is often suspected because of the wide range of disease problems it causes. This variety of clinical signs has complicated the diagnosis of this viral infection because there are no simple answers. It is, however, essential that a definitive diagnosis be made before costly control measures are implemented.