Children who receive peritoneal dialysis (PD) are at increased risk for thyroid dysfunction. A rarely appreciated cause is iodine overload. We report 4 children who developed iodine overload and secondary hypothyroidism. All had kidney failure treated by PD. Each previously had normal thyroid function screening test results. At the time hypothyroidism was detected, the duration of PD ranged from 1 week to 27 months (median, 6 months). Three children had high thyrotropin values and all had high serum iodine levels.