We present the case of a 74 year old patient suffering from primary Non Hodgkin's lymphoma of the thyroid and Sjogren's syndrome. A massively enlarging goitre, causing breathlessness in a female patient previously treated for autoimmune inflammation of the thyroid (Hashimoto's disease) and Sjogren's syndrome, indicated the need for a fine needle aspiration biopsy (FNA) of the thyroid gland. Non Hodgkin's lymphoma of the thyroid was diagnosed and chemotherapy was begun. After 10 months of cytostatic treatment clinical tests and imaging indicated complete local regression. However, two months after cessation of chemotherapy the patient suffered a relapse of the disease owing to infiltration of the central nervous system. During the course of palliative radiotherapy the patient died. The main purpose for presenting this case was to describe the problem of primary lymphoma of the thyroid in cases of autoimmune disease. As many years of immunisation may lead to carcinogenesis it is important to raise awareness among medical staff with regard to cases of chronic autoimmune disease. In cases of Hashimoto's autoimmune disease of the thyroid, monitoring of the anti-thyroid antibodies is indicated, at least annually, as an increase in the concentration of these antibodies over a period of at least seven years would suggest further development of autoimmune disease. If such conditions are accompanied by tumours of the thyroid, surgery should be considered. It is worth keeping in mind that the thyroid can be a site for extra-lymphatic lymphoma.