Clinical features and outcomes of extranodal natural killer/T-cell lymphoma (ENKL) arising from extranasal sites are not fully understood. The purpose of this study was to study the prognosis and treatment outcome of skin/soft tissue primary ENKL. This multicenter retrospective study included 48 patients with skin/soft tissue primary ENKL diagnosed from 1993 to 2010. Patients with Ann Arbor stage I, T1–2N0M0 by International Society for Cutaneous Lymphomas–European Organization of Research and Treatment of Cancer TNM (tumour–node–metastasis) stage, International prognostic index score of 0–1, and a Korean prognostic index (KPI) score of 0–1 were associated with better survival. Four of five patients with T1–2N0M0 disease achieved complete response with radiation alone. In disseminated disease, only 6 of 13 patients responded to anthracycline-containing chemotherapy, and all the two patients receiving SMILE showed response. In conclusion, we identified the prognostic value of KPI, and we suggest a treatment recommendation according to the TNM (tumour–node–metastasis) stage. Radiotherapy with/without chemotherapy seemed to be optimal in localized disease. In advanced stages, a more aggressive treatment regimen with newer agents should be sought.