Transient hypothyroidism was observed in 5 children aged 6 to 14 years with chronic lymphocytic thyroiditis. In two cases, all thyroid function tests showed definite hypothyroid status and returned to normal range within a few months. The titer of thyroid autoantibodies did not change in these periods. In another two cases, the blood thyroid hormone levels were found to be lowest at the first examination and became normal within one or two months. In one more case, thyroid function tests were found to be hypothyroid range at 9 years of age during the course of the disease from 3 years of age and she was supplemented with desiccated thyroid only for six months. Thereafter she has remained in euthyroid status. It is suggested that transient hypothyroidism might be a common finding in girls suffering from chronic lymphocytic thyroiditis. The pathogenesis remains obscure.