Background: Mature T-cell and natural killer (NK)-cell lymphomas compose a heterogeneous group of non-Hodgkin lymphomas, and extranodal NK/T-cell lymphoma, nasal type (ENKTL) is an aggressive subtype with sporadic CD30 expression. However, the significance of CD30 expression in ENKTL is controversial. We aimed to classify a large cohort of patients with mature T-cell and NK-cell lymphomas according to the 2016 World Health Organization (WHO) classification guidelines and to study the association between CD30 expression and prognosis of patients with ENKTL. Methods: We selected consecutive patients with mature T-cell and NK-cell lymphomas who attended our institution between September 1, 2009 and August 31, 2013. We classified the lymphomas according to the 2016 revision of the WHO classification of lymphoid neoplasms, analyzed the associations between CD30 expression and clinicopathologic features of ENKTL patients, and evaluated the prognostic implications of CD30 expression. Results: We identified 622 consecutive patients with mature T-cell and NK-cell lymphomas, including 317 (51.0%) patients with ENKTL. In addition, CD30 expression was detected in 43 (47.3%) of a subset of 91 patients with ENKTL. No clinicopathologic features were associated with CD30 expression, and CD30 positivity showed no prognostic significance in patients with ENKTL. Conclusions: ENKTL is the most common type of mature T-cell and NK-cell lymphoma diagnosed at our institution. CD30 is frequently expressed in ENKTL and represents a therapeutic target; however, it may not be a prognostic marker.