The proportion of aggressive T/NK-cell lymphoma in Korea is larger than in the West, and it shows a lower response to conventional chemotherapy and poorer survival than diffuse large B-cell lymphoma. This study was undertaken to evaluate the response rate and survival and to document the prognostic factors in patients with T/NK-cell lymphoma who have undergone high-dose therapy (HDT). Eligibility for the study was a mature T/NK-cell lymphoma with initially poor risk (as high or high intermediate risk on age-adjusted International Prognostic Index) or relapsed cases. Twenty-eight patients from 6 centers were reviewed retrospectively. The M : F ratio was 20:8, and median age was 36 years (range 16--60 years). Twelve patients had unspecified peripheral T-cell lymphomas, 7 anaplastic large-cell lymphomas, 6 nasal T/NK-cell lymphomas, and 3 angioimmunoblastic T-cell lymphomas. Disease status at transplant were initially poor risk in 15, chemosensitive relapse in 8 and chemo-resistant relapse in 5 patients, respectively. A complete response (CR) after HDT comprised 20 patients, including 16 with continued CR. Absolute neutrophil count ( > 500/microl) recovered at a median 11 days after autologous stem cell transplantation in 26 patients. Two therapy-related mortalities occurred. Estimated 3-year event-free survival and overall survival (OS) (+/- SE) were 24+/- 9 and 42+/- 10 months, respectively. Only CR status after HDT influenced OS (P=0.000). Therefore, an initial approach with effective induction and HDT may result in a better outcome in T/NK-cell lymphoma.