Published data on the influence of hypothyroidism on fertility, gestation, and the offspring are controversial. We studied nine hypothyroid women during 11 pregnancies. Mean serum values for thyroxine, triiodothyronine (T3), resin T3 uptake ratio, and thyroid-stimulating hormone were 2.3 μg/dL, 82 ng/dL, 0.64, and 105 mU/mL, respectively. Four patients had iatrogenic hypothyroidism (three remote thyroidectomy, one remote 131I therapy), two Hashimoto's thyroiditis, and three idiopathic primary hypothyroidism. Seven patients first presented untreated after the 24th week of gestation. Two patients needed cesarean section; seven delivered vaginally. There was one stillborn infant in the only patient with pre-eclampsia. Another infant had Down's syndrome and an ostium primum defect (mother's age, 41 years). The remaining nine infants were normal at birth. All placentas were normal. Follow-up in seven infants up to 2.7 years showed normal thyroid function and somatic development. Infants of hypothyroid mothers may be normal because their hypothalamic-pituitary thyroid axis develops independently from the mother.