Purposes: 1- To evaluate the specificity of PET/CT in initial diagnosis of Non-Hodgkin's lymphoma. 2- To assess the value of PET/CT scan in staging Non-Hodgkin's lymphoma. Subjects: The author enrolled 21 patients diagnosed Non-Hodgkin's lymphoma (histopathology confirmed) from June 2010 to June 2011. All the patients have been underwent PET/CT in The Nuclear Medicine and Oncology center, Bach Mai hospital. Results: 1- Specificity of PET/CT in Non-Hodgkin's lymphoma: PET/CT revealed lesions in 16 positions, most common were: neck lymph nodes (33,3 percent), mediastinal lymph nodes (28,6 percent), abdominal lymph nodes (23,8 percent), axillary lymph nodes (14,3 percent), and a lower percentage for other positions. FDG uptake (SUV max) of the lesions: brain tissue (15,24), post-ocular (11,35), adrenal gland (11,34), etc. WF4-7 group has average SUV of 9,92-15,33 which is higher than WF2-3 group (6,23-7,18). 2. The value of PET/CT scan in staging Non Hodgkin's lymphoma: PET/CT scan changed the stage of 5/21 (23,8 percent) patients. Conclusion: PET/CT is very useful in initial diagnosis and staging Non Hodgkin's lymphoma. Overall survival benefit and patient quality of life during and after treatment may also be optimized with tailored therapy defined by more accurate staging with PET/CT.