Abstract: Objective To explore the value of 18F-FDG PET/CT in the diagnosis and treatment evaluation in patients with pretreatment or recurrent extranodular natural killer/T-cell lymphoma nasal type (ENTCL). Methods 18F-FDG PET/CT images and clinical records of 35 cases (67 scans) of pathologically confirmed ENTCL treated in our hospital within the last 9 years were analyzed. The imaging characteristics of the upper aerodigestive tract (UAT) and the non-aerodigestive tract (NUAT) lesions were analyzed. Lesion distribution, clinical stages, SUVmax and patient survival data were compared between pretreatment and recurrent cases. Results All the ENTCL lesions were hypermetabolic. The UAT lesions involved mainly the nasal cavity and pharynx, while the NUAT lesions may involve the lymph nodes and all the organs. UAT lesions were more common in pretreatment cases while NUAT lesions tended to increase in recurrent cases. The SUVmax of pretreatment and recurrent lesions were 10.4 ± 4.4 and 9.6 ± 5.2, and showed no significant difference among patients with different lesion distribution patterns, clinical stages, or treatment history. The tumor remission rate evaluated by PET/CT were higher in cases with an initial diagnosis than in those with recurrence［(89.5% (17/19) vs 33.3% (5/15), P<0.005)］. Cox regression analysis revealed no significant differences in the survival rates among patients with different treatment history, clinical stages, lesion distribution patterns, or SUVmax levels (P>0.05). Conclusion 18F-FDG PET/CT can sensitively detect the pretreatment or recurrent lesions in ENTCL patients and helps in accurate tumor staging and curative effect evaluation.