SUMMARYThe Authors describe a pair of dizygotic twins of different sex, affected by hemolytic disease of the newborn in form of nuclear icterus. On the basis of the different severity of the disease, the Authors underline the role played not only by the immunization degree of the mother, by the type of the produced antibodies and by the placental filtration, but also by other fetal factors. Oculogyric crises and Cantelli's sign, observed up to now only in Parkinson's disease, are for the first time related to the nervous lesions induced by the icterus.