The aim of the study was to investigate the incidence of thyroid abnormalities in neck irradiated lymphoma patients. Of the 298 patients who had irradiation to the neck for lymphoma between 1966-1988, 174 were found to be alive and free of disease. These patients were invited to participate in the study. From the 174, 93 were able to participate (group 1). Two control groups were recruited; both were sex and aged matched. One group (group 2) consisted of lymphoma patients who were treated with chemotherapy (n=39) or irradiation to areas other than the neck (n=16). The other group (group 3) consisting of healthy volunteers (n=35) recruited from hospital staff and minor surgery attendees, had never had lymphoma or radiotherapy. All participants were required to complete a past medical history and thyroid symptom questionnaire, had blood taken for assays of thyroid stimulating hormone (TSH), thyroglobulin antibodies, thyroid peroxidase antibodies, sodium iodide symporter antibodies and TSH receptor antibodies and underwent ultrasound and clinical examination of the neck. A significant percentage of patients who had been irradiated in the neck had abnormalities on ultrasound, compared to groups 2 and 3 (77% vs 42% vs 24%). Abnormal TSH levels were found to be significantly more common in neck irradiated patients compared to the other groups (50% vs 9% vs 5%). There is a clear difference between neck irradiated patients and control groups. The importance of screening irradiated patients for thyroid abnormalities is re-emphasised.