In reviewing the clinical literature reporting pregnancy in women with hypothyroidism since 1897, a distinction has been made between those treated to some degree by thyroid extracts or hormones, and those untreated. Abortions and stillbirths are more frequent in those untreated. Normal offspring are more common in mothers who were treated. Congenital anomalies occur approximately equally in offspring of both treated and untreated women but at a rate of more than 19 per cent of all live births. These findings are relevant particularly to those at risk in areas of endemic iodine deficiency.