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Aim/Introduction: One of the most dire complications of hematopoietic stem cell (HSCT) and solid organ transplantation (SOT) is the development of post-transplant lymphoproliferative disorder (PTLD). PTLD compromises a broad spectrum of disorders classified by the 2017 World Health Organization (WHO) in non-destructive, polymorphic, monomorphic and classic Hodgkin lymphoma. Distinct morphologies are associated with a more favorable clinical course and better response to initial treatment. Reduction of immunosuppression, commonly used as first-line treatment, has been associated with higher response rates in non-destructive and polymorphic PTLD, while a more aggressive therapy is advised for monomorphic PTLD. Biopsy is the reference standard for PTLD diagnosis and classification, but may not always be safely possible. Therefore, there is a need for non-invasive imaging-based tools. Materials and Methods: All patients with histopathologically proven PTLD at the UMC Groningen were included in this study between January 2010 to March 2019. FDG-PET/CT scans were performed on a Siemens Biograph mCT camera, according to EANM procedure guidelines for tumor imaging and reconstruction parameters compliant with EARL recommendations. Semi-quantitative measurements (SUVmax, SUVpeak and SUVmean) were performed using dedicated Hermes Hybrid 3D software with the ?Tumor Finder? application. Semi-quantitative measurements were obtained from the biopsy site or in cases in which a biopsy was performed before the scan from the nearest lymph node in the same lymph node region Results: In total 41 patients were included. From those, 27 were monomorphic PTLD and 14 were ?other PTLD morphologies?, including non-destructive (n=4), polymorphic (n=9) and Hodgkin-like PTLD (n=1). Median SUVmax, SUVpeak, SUVmean values were statistically significantly higher in monomorphic PTLD than in ?other PTLD morphologies (p