Huntington’s disease (HD) is a neurodegenerative disease characterized in part by the loss of striatopallidal medium spiny projection neurons (MSNs). Expression of BDNF and noggin via intracerebroventricular (ICV) delivery in an adenoviral vector triggers the addition of new neurons to the neostriatum. In this study, we found that a single ICV injection of the adeno-associated viruses AAV4-BDNF and AAV4-noggin triggered the sustained recruitment of new MSNs in both wild-type and R6/2 mice, a model of HD. Mice treated with AAV4-BDNF/noggin or with BDNF and noggin proteins actively recruited subependymal progenitor cells to form new MSNs that matured and achieved circuit integration. Importantly, the AAV4-BDNF/noggin-treated R6/2 mice showed delayed deterioration of motor function and substantially increased survival. In addition, squirrel monkeys given ICV injections of adenoviral BDNF/noggin showed similar addition of striatal neurons. Induced neuronal addition may therefore represent a promising avenue for disease amelioration in HD.