An eight year old female intact Holstein cow presented with lethargy, recumbency, diarrhea, and fever. The cow was five months carried calf, dry and on pasture. A diagnosis of bovine leukosis virus associated lymphosarcoma was made based on clinical presentation, gross necropsy findings and a positive BLV AGID test. This paper will address causes of lymphosarcoma in dairy cattle, the pathogenesis of the bovine leukosis virus (BLV), treatment options, economic implications of BLV infection and control methods.