Relapse of acute lymphoblastic leukemia (ALL) remains a major therapeutic challenge. Despite the consensus for proceeding to allogeneic stem cell transplantation (HSCT) in relapsing patients with ALL who achieve second complete remission (CR2) with salvage therapy, most patients lack a suitable matched-related histocompatible donor. The present multicenter retrospective study compared, for ALL patients in CR2, the HSCT outcome from all four possible alternative hematopoietic stem cell sources, namely matched unrelated 10/10 (n = 281), mismatched unrelated 9/10 (n = 125), haploidentical (n = 105), and cord blood (n = 104) donors. The 2-year outcomes were not statistically different between the four donor sources with respect to overall survival (38.3-47.2%), leukemia-free survival (30.5-39.6%), relapse incidence (32.6-37.6%), nonrelapse mortality (27.5-34.6%), and graft-versus-host disease-free relapse survival (21.4-33.1%). Donor choices for ALL patients achieving CR2 post first relapse are broad, ensuring that most patient in need secures a graft. Therefore, in practice, the donor choice should depend on timely availability and policy center.