Adult stem cells are essential for tissue homeostasis and wound repair. Their proliferative capacity must be tightly regulated to prevent the emergence of unwanted and potentially dangerous cells, such as cancer cells. We found that mice deficient for the proapoptotic Sept4/ARTS gene have elevated numbers of hair follicle stem cells (HFSCs) that are protected against apoptosis. Sept4/ARTS(-/-) mice display marked improvement in wound healing and regeneration of hair follicles. These phenotypes depend on HFSCs, as indicated by lineage tracing. Inactivation of XIAP, a direct target of ARTS, abrogated these phenotypes and impaired wound healing. Our results indicate that apoptosis plays an important role in regulating stem cell-dependent regeneration and suggest that this pathway may be a target for regenerative medicine.