Replacement of damaged neuronal population by fetal tissue transplantation represents a potential treatment for neurodegenerative diseases. Consistent success has been achieved with fetal striatal transplantation in Huntington's disease animal models and patients. We report the neo-generation of metabolically active tissue with striatum-like imaging features after transplantation of striatal primordia in a patient with Huntington's disease. This study represents the first "in vivo" demonstration that a human striatal anlagen, transplanted into the adult human brain, is able to progress in its development and to generate a new anatomical structure in the host, without evidence of neoplasia or teratoma.