Peripheral unspecified T-cell lymphoma not otherwise specified (PTCL NOS) is a malignant neoplasm that develops from mature T-lymphocytes and NK cells. PTCL NOS is a rare malignant neoplasm that occurs most often in men, predominantly over 60 years of age. This type of lymphoma accounts for about 15% of all non-Hodgkin’s lymphomas. The paper describes a clinical case of PTCL NOS , which was difficult to diagnose.