In 1994, in a large parcel depot in the north of England employing 600 staff and 24 electrical and mechanical engineers, two engineers developed papillary cell carcinoma of the thyroid in the same year. A comprehensive review of the literature revealed that ionizing radiation is the only known direct cause of this disease. There was speculation that air filter changing undertaken by the two men affected, shortly after the Chernobyl accident in 1986, may have exposed them to concentrated radioactive fallout. A radiation survey of the parcel depot was undertaken and revealed no evidence of abnormal radioactivity. A total of 27 past and present engineering staff were screened for thyroid cancer. No cases of thyroid cancer were found. Investigation of clusters of rare disease in the occupational setting is indicated mainly in order to address the concerns of the workforce. Nevertheless, investigation is warranted, especially when the aetiology of a disease is poorly understood. It would be prudent for doctors, in whatever speciality, to take an occupational history from individuals who develop thyroid cancer.