Authors report the cases of a boy with a Menkes' disease which began by a convulsive encephalopathy at the age of two months with growth failure and metaphysical abnormalities. An oldest brother died at 2 years of age in an analogous scene. The diagnosis proved to be founded by the low serum copper and coeruleo-plasmia levels and by the increased uptake of copper in the cultured skin-fibroblasts. The hair was thin and kinky; microscopical study showed pili torti and trichorrhexis nodosa. For the following pregnancy of the mother, a prenatal diagnosis by precocious amniocentesis (amniotic fluid punction) allowed to say that the boy she was expecting for was clear of the disease because of the normal uptake of copper 64 Cu in cultured amniotic fluid cells of the foetus. Authors recall that Menkes' disease is a X linked recessive disorder beginning by epileptic seizure in the early months of life. The basic biochemical lesion of copper metabolism is unknown; there are abnormalities in copper and his binding protein (metallothionein) distribution with increased level is the kidney and decreased level in brain and liver. The copper therapy does not lead to clinical improvement. There is now a prenatal diagnosis: the study of copper uptake in cultured amniotic fluid cells of male fetus. It is abnormally increased in Menkes' disease.