Hypothyroidism due to insufficient iodine intake is a rare nutritional disorder in Japan, where marine products containing plenty iodine are consumed. The daily requirement of iodine is suggested to be from 150 to 200 μg while the average iodine intake in Japan is 1 mg per day. However, hypothyroidism due to insufficient iodine intake has become one of the important problems for the individuals who require gastric tube feeding for a long time, as the number of such cases recently increases. In this study, we examined the thyroid function of 9 individuals on long term gastric tube feeding (mean duration, 3 years), who had been admitted to our institution during 2001–2007. The ages of the individuals at the study were 3 to 30 years old (mean age, 11 years). Two patients had hypothyroidism due to iodine deficiency which is characterized by low fT4 with normal fT3. One of the patients with hypothyroidism presented a diffuse goiter and myxedema. The daily iodine intake in the 2 patients was 15.2 and 6.4 μg per day, respectively. Immediately after initiation of iodine supplementation, both patients retrieved euthyroid function. Doctors and caretakers should be aware of the risk of iodine deficiency associated with long term gastric tube feeding and appropriate amount of iodine should be supplemented if necessary, since over intake of iodine may also result in thyroid dysfunction. It is suggested that the monitoring of various trace elements including iodine is indispensable for the individuals on long term gastric tube feeding.