Peripheral T lymphomas are formed by cells with CD3 antigen which contain TCR alpha/beta. A minor part of the non-tumourous population contains TCR gamma/delta. The position is similar in T cell tumours. In the tumours however TCR may be lacking .NK ("natural killer") cells are CDR3 negative, rearrangement of the gene TCR does not occur and they are TCR alpha/beta and TCR gamma/delta negative. Contrary to T cells they contain antigen CD56 ("NK-associated anti- gen").In these cells and in tumours cytotoxic proteins are usually present: TIA-1, granzyme-B, perforin. There is a continuous transition between T and NK cells. The prognosis of T cell tu- mours cannot be assessed from the cell size. T/NK small cell lymphomas are highly aggressive tumours. The prognosis of patients is very bad. From the morphological aspect they can resemble very much non-tumorous lymphocytes. Conversely, large cell T lymphomas of the skin which are CD30 positive take a very mild course and their prognosis is favourable. The author mentions also some more recent entities of extranodular T lymphomas : angiocentric NK/T lymphoma of the nose (and other regions), malignant T cell lymphoma in enteropathies, T cell lymphoma resem- bling subcutaneous panniculitis, hepatosplenic gamma/delta T lymphoma.These tumours are rare in this country and some, e.g. T/NK lymphoma of the nose, are found usually only in certain regions of the world. They may be however encountered also in Europe, in particular in immuno- suppressed subjects and patients after organ transplantation.

        Key words: T/NK lymphoma - extranodular T lymphoma - immunohistology