PET/CT whole-body imaging, as a new diagnostic tool in recent years, is of great value in the diagnosis, staging and monitoring of the efficacy of lymphoma, and is superior to the comprehensive evaluation made by conventional imaging. Its clinical application can change the treatment plan of some lymphoma patients and thus improve the diagnosis and treatment of lymphoma. PET/CT and the diagnosis and differential diagnosis of lymphoma Accurate diagnosis and staging of lymphoma are crucial to the selection of appropriate treatment. 18F-FDG PET/CT imaging is based on the characteristics of increased glucose metabolism in malignant tumors and has important reference value for the diagnosis of lymphoma. Current domestic and international literature shows that PET/CT has a high positive detection rate for common subtypes such as Hodgkin’s lymphoma (HL), follicular lymphoma, diffuse large B-cell lymphoma, and condyloma, while the positive detection rate for rare subtypes such as marginal zone lymphoma, peripheral T-cell lymphoma, mucosa-associated lymphoma, extra-nodal marginal zone B-cell lymphoma, and Burkitt’s lymphoma is relatively low. PET/CT and staging and restaging of lymphoma Staging of lymphoma refers to the assessment of the disease before treatment, while restaging refers to the further evaluation of the efficacy after treatment. Accurate staging is the basis for treatment planning and prognosis, especially for defining the population and site of HL suitable for radiotherapy. Therefore, NCCN recommends the option of staging and restaging patients with lymphoma using 18F-FDG PET. PET/CT and treatment outcome evaluation of lymphoma Accurate identification of residual masses and recurrence after tumor treatment is extremely meaningful for the development of treatment plans. Residual lesions of lymphoma after radiotherapy still take up FDG, while fibrous scar tissue does not take up FDG and is negative for PET. The sensitivity and specificity of PET in detecting lymphoma with residual masses after chemotherapy were found to be 50% and 69%, respectively, and those with negative masses on PET did not require further radiotherapy, thus avoiding unnecessary treatment. A meta-analysis in 2008 suggested that PET/CT is an effective tool for evaluating residual masses for tumor cells in HL with residual masses after completion of first-line therapy; the 2009 National Comprehensive Cancer Network (NCCN) guidelines recommend that patients with HL undergo PET/CT after completion of all treatments to evaluate the presence of residual lesions, and positive lesions can be retrieved for Biopsy. A 2006 meta-analysis (15 studies) showed that the overall sensitivity and specificity of PET/CT for detecting residual lesions in HL was 84% and 90%, respectively, and for detecting NHL was 72% and 100%, respectively. A 2009 meta-analysis showed that for higher-grade HL, PET/CT at mid-treatment is an effective predictor of patient prognosis, detecting those who are insensitive to chemotherapeutic agents, but for diffuse large B-cell lymphoma, there is still insufficient evidence to suggest that PET/CT should be routinely performed at mid-treatment.