Lymphoma is one of the most commonly diagnosed malignancies in dogs, and now represents a significant proportion of all cases seen at veterinary hospitals in North America. A number of modalities are currently used to diagnose and clinically stage this disease. Lymphoma can manifest itself in a variety of ways when present in the thorax. Some of these variations may provide insight into the natural behavior of the disease and the animal's prognosis. A number of factors have been implicated in the cause of canine lymphoma and its prognostication. The goal of this paper is to explore the many facets of thoracic lymphoma and review a number of diagnostic and therapeutic modalities used in treating this disease while reviewing a clinical lymphoma case.