Objective To investigate the clinical value of F-18-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (F-18-FDG PET/CT) in IgG4-related disease (IgG4-RD). Methods Seventy two patients diagnosed with IgG4-RD who underwent PET/CT were included. Correlations between clinical variables and PET/CT findings were analyzed by Spearman's correlation test. Conventional radiology was compared to PET/CT to evaluate detection discrepancies. The detection ability of insidious organ involvement by PET/CT at disease onset was investigated. The utility value of PET/CT for the 2019 ACR/EULAR classification criteria was analyzed with the multivariate logistic analysis and ROC curve. Results SUVmax of main involved organ was positively correlated with IgG4-RD Responder Index (IgG4-RD RI), serum and tissue IgG4 levels and IgG4/IgG ratio, serum eosinophils counts and number of involved organs, while negatively correlated with serum IgM levels. PET/CT was superior in detecting organ/tissue involvements including prostate, gastrointestinal tract and lung compared with conventional imaging. For patients with pancreato-hepato-biliary or head-neck involvements at onset, PET/CT showed superiority in detecting insidious lesions. Multivariate analysis showed that disease duration, multiple-organ involvement, SUVmax of main involved organ and mean SUVmax of all involved organs were significantly associated with the fulfillment of the 2019 ACR/EULAR classification criteria. ROC curves indicated that the cut-off value for SUVmax of main involved organ and mean SUVmax of all involved organs for fulfillment of the 2019 ACR/EULAR classification criteria for IgG4-RD were 4.1 and 3.5, respectively. Conclusion F-18-FDG PET/CT has potential capacity to monitor disease activity, evaluate organ involvements and assist in the classification criteria in IgG4-RD.