Fallibility of postal questionnaire follow-up for detection of hypothyroidism after iodine-131 therapy.

Four hundred and twelve patients who received radioactive iodine for thyrotoxicosis were followed up for periods from one to three years by postal questionnaire. Hypothyroidism was detected in only three instances, and, despite intensive efforts to trace subjects, 41% of them were lost to follow-up because of either failure to participate or change of address over three years. It is apparent that a postal questionnaire is an unsatisfactory method for following up a Melbourne inner-suburban population over a prolonged period.