Lymphoma represents the most common malignant tumour in cats. Genetic factors, retrovirusinfections, chronic inflammation, immunosuppression and passive smoking are discussed as possible causes. Clinical signs at presentation normally depend on the anatomic site of the tumour. The alimentary form occurs most frequently with an increasing incidence, followed by extranodal, nodal and mediastinal lymphoma. Cytology is an important diagnostic tool and samples can be obtained by ultrasound-guided fine needle aspiration and thoracocentesis. For the most part the tentative diagnosis can be confirmed by the results of the cytological examination, however a histopathologic examination is essential for establishing a state of the art diagnosis. At present a reorganisation of the pathohistologic classification systems takes place, replacing the older WF (Working Formulation) for the newer REAL/WHO (revised European-American Classification of Lymphoid Neoplasms/World Health Organisation) Classification. The latter evaluates not only the morphology but includes also the immunophenotype of neoplastic cells. The cornerstone of lymphoma treatment, prevalently a systemic disease, is chemotherapy, which in general is tolerated mostly well by cats. Radiation therapy has proven successful especially in nasal lymphoma. Its usefulness in all other forms is not known yet. Additionally, the impact of sugery as part of therapy is still unclear, with insufficient studies performed. Prognosis of nasal or nodal lymphoma appears to be fair to good, cats showing a prolonged survival of about 1 to 2 years. Mediastinal, spinal, renal and alimentary lymphomas have a less favourable prognosis, median survival times of less than 6 months are quite common.