Natural killer (NK) cell lymphomas are rare malignancies. They are classified as extranodal NK/T-cell lymphoma, nasal type, and aggressive NK cell leukemia. NK cell neoplasms are prevalent in Asian and South American populations, but are extremely rare in the West. They can be classified clinically into nasal, non-nasal, and aggressive lymphoma/leukemia subtypes. For nasal NK cell lymphomas, combined chemotherapy and radiotherapy are indicated for stage I/II disease. Chemotherapy is the main treatment for stage III/IV nasal NK cell lymphomas, as well as the non-nasal and aggressive subtypes. Regimens containing drugs not affected by the P-glycoprotein, particularly in combination with L-asparaginase, have resulted in much improvement in treatment outcome for high-risk, refractory or relapsed patients. Autologous or allogeneic hematopoietic stem cell transplantation should be considered for selected patients. Epstein-Barr virus DNA load as a surrogate marker for prognostication, and clinical stratification of patients should be incorporated in clinical management algorithms.