Abstract Hematopoietic cell transplantation (HCT) has become standard-of-care for an increasing number of inborn errors of immunity (IEI). This report is the first to compare transplant outcomes according to T-cell–replete (ie, T-replete) HLA-matched grafts using alemtuzumab (n = 117) and T-cell–depleted (ie, T-depleted) HLA-mismatched grafts using T-cell receptor-αβ (TCRαβ)/CD19 depletion (n = 47) in children with IEI who underwent first HCT between 2014 and 2019. All patients received treosulfan-based conditioning except patients with DNA repair disorders. For T-replete grafts, the stem cell source was marrow in 25 (21%) patients, peripheral blood stem cell (PBSC) in 85 (73%), and cord blood in 7 (6%). TCRαβ/CD19 depletion was performed on PBSCs from 45 haploidentical parental donors and 2 mismatched unrelated donors. The 3-year overall survival (OS) and event-free survival for the entire cohort were 85% (77%-90%) and 79% (69%-86%), respectively. Analysis according to age at transplant revealed a comparable 3-year OS between T-replete grafts (88%; 76%-94%) and T-depleted grafts (87%; 64%-96%) in younger patients (aged <5 years at HCT). For older patients (aged >5 years), the OS was significantly lower in T-depleted grafts (55%; 23%-78%) compared with T-replete grafts (87%; 68%-95%) (P = .03). Grade III to IV acute graft-versus-host disease was observed in 8% of T-replete marrow, 7% of T-replete PBSC, 14% of T-replete cord blood, and 2% of T-depleted PBSC (P = .73). Higher incidence of viremia (P < .001) and delayed CD3 reconstitution (P = .003) were observed after T-depleted graft HCT. These data indicate that mismatched donor transplant after TCRαβ/CD19 depletion represents an excellent alternative for younger children with IEI in need of an allograft.