G ene-based delivery can establish a sustained supply of therapeutic proteins within the nervous system. For diseases characterized by extensive CNS and peripheral nervous system (PNS) involvement, widespread distribution of the exogenous gene may be required, a challenge to in vivo gene transfer strategies. Here, using lentiviral vectors (LVs), we efficiently transduced hematopoietic stem cells (HSCs) ex vivo and evaluated the potential of their progeny to target therapeutic genes to the CNS and PNS of transplanted mice and correct a neurodegenerative disorder, metachromatic leukodystrophy (MLD). We proved extensive repopulation of CNS microglia and PNS endoneurial macrophages by transgene-expressing cells. Intriguingly, recruitment of these HSC-derived cells was faster and more robust in MLD mice. By transplanting HSCs transduced with the arylsulfatase A gene, we fully reconstituted enzyme activity in the hematopoietic system of MLD mice and prevented the development of motor conduction impairment, learning and coordination deficits, and neuropathological abnormalities typical of the disease. Remarkably, ex vivo gene therapy had a significantly higher therapeutic impact than WT HSC transplantation, indicating a critical role for enzyme overexpression in the HSC progeny. These results indicate that transplantation of LV-transduced autologous HSCs represents a potentially efficacious therapeutic strategy for MLD and possibly other neurodegenerative disorders.