Background: Current standard treatment, including non-anthracycline-based chemotherapy and optimal combining of radiotherapy, has dramatically improved outcomes of patients with extranodal natural killer/T-cell lymphoma (ENKTL) during the last decade. This study was conducted to investigate the clinical outcome of ENKTL patients with relapsed or progressive disease after initial current standard therapy. Patients and methods: We retrospectively reviewed patients diagnosed with ENKTL at six centers in four countries (China, France, Singapore, and South Korea) from 1997 to 2015 and analyzed 179 patients who had relapsed or progressed after initial current standard therapy. Results: After a median follow-up of 58.6 months (range 27.9-89.2), the median second progression-free survival (PFS) was 4.1 months [95% confidence interval (CI) 3.04-5.16] and overall survival (OS) was 6.4 months (95% CI 4.36-8.51). Multivariate Cox-regression analysis revealed that elevated lactate dehydrogenase, multiple extranodal sites (>= 2), and presence of B symptoms were associated with inferior OS (P < 0.05). OS and PFS were significantly different according to both prognostic index of natural killer lymphoma (PINK) and PINK-E (Epstein-Barr virus) models. Salvage chemotherapy with L-asparaginase (L-Asp)-based regimens showed a significantly better clinical benefit to response rate and PFS, although it did not lead to OS improvement. First use of L-Asp in the salvage setting and L-Asp rechallenge at least 6 months after initial treatment were the best candidates for salvage L-Asp containing chemotherapy. Conclusions: Most patients with relapsed or refractory ENKTL had poor prognosis with short survival. Further studies are warranted to determine the optimal treatment of patients with relapsed or refractory ENKTL.