LONG-TERM follow up of children born to thyrotoxic mothers treated with propylthiouracil (PTU) during pregnancy has not been reported previously. Since the goiters in the newborn associated with PTU therapy are usually small and, unlike iodide goiters, do not cause mechanical difficulties,1the major concern is whether the presence of goiter with accompanying hypothyroidism has an adverse effect on subsequent intellectual and physical development. This in turn is part of the larger question as to whether PTU therapy in the pregnant patient with thyrotoxicosis has any harmful effects on the subsequent development of the offspring. In an effort to answer this question, children whose mothers had received PTU during pregnancy were studied and compared to siblings who were born at a time when the mothers were not receiving PTU and who were presumably euthyroid. Materials and Methods From a previously reported group of 37 children whose mothers had received