Natural killer/T-cell lymphomas (NKTCL) represent rare and aggressive lymphoid malignancies. Patients (pts) with relapsed/refractory disease after Asparaginase (ASPA)-based chemotherapy have a dismal prognosis. To better define the role of allogeneic hematopoietic stem cell transplantation (allo-HSCT), we conducted a retrospective analysis of data shared with the European Society for Blood and Marrow Transplantation (EBMT) and cooperating Asian centers. We identified 135 pts who received allo-HSCT between 2010 and 2020. Median age was 43.4 years at allo-HSCT, 68.1% were male. Ninety-seven pts (71.9 %) were European, 38 pts (28.1%) Asian. High Prognostic Index for NKTCL (PINK) scores were reported for 44.4%; 76.3% had >1 treatment, 20.7% previous auto-HSCT, and 74.1% ASPA-containing regimens prior to allo-HSCT. Most (79.3%) pts were transplanted in CR/PR. With a median follow-up of 4.8 years, 3-year progression-free(PFS) and overall survival were 48.6% (95%-CI:39.5-57%) and 55.6% (95%-CI:46.5-63.8%). Non-relapse mortality at 1 year was 14.8% (95%-CI:9.3-21.5%) and 1-year relapse incidence 29.6% (95%-CI:21.9-37.6%). In multivariate analyses, shorter time interval (0-12 months) between diagnosis and allo-HSCT [HR = 2.12 (95%-CI:1.03-4.34); P = 0.04] and transplantation not in CR/PR [HR = 2.20 (95%-CI:0.98-4.95); P = 0.056] reduced PFS. Programmed cell death protein 1(PD-1/PD-L1) treatment before HSCT neither increased GVHD nor impacted survival. We demonstrate that allo-HSCT can achieve long-term survival in approximately half of pts allografted for NKTCL.