We report on a case of fetal goitrous diagnosed on ultrasonogram done at 31 weeks of gestation. Thyroid maternal function was normal and no therapeutic was responsible. Hormonal test done on cord blood supported diagnosis of prenatal hypothyroidism. The infant was born prematurely at gestation age of 34 without antenatal treatment. He was eutrophic with clinical and biological signs of hypothyroidism and a large goiter. Therapy with thyroxine was instituted on the third day of life. At 9 months, growth and development are normal. Congenital hypothyroidism has an incidence of approximately 1 in every 4000-5000 live births. Rarely fetal goitrous hypothyroidism have been attributed to thyroid hormone dyshormonogenesis. When fetal goiter is diagnosed on ultrasonography, without maternal hypothyroidism or therapeutic and when hypothyroidism is confirmed on fetal blood, this diagnosis must be suspected.