The malignant lymphomas are an heterogeneous group of diseases, manifest most frequently by the development of painless lymphadenopathy with or without splenomegaly and sometimes associated with constitutional symptoms. The natural history of these conditions is one of progressive increase in lymphadenopathy, both in terms of size and the number of sites, with death occurring from intercurrent infection or as a consequence of compression of a vital organ by lymph nodes. Spontaneous regression, although it has been reported, is very rare. The rate of progression, and the specific sites most frequently involved, vary with the specific subtype of lymphoma in question. Happily, the natural history is rarely observed nowadays since treatment is available which may cure a significant proportion of patients and be of very considerable palliative benefit to others. Their importance to the physician lies in the fact that, as a group, they are the seventh commonest malignancy in the United Kingdom, they afflict a relatively young population and have become potentially curable.