False positive findings in primary tumor and metastasis diagnostics by FDG-PET due to FDG-uptake in inflammatory foci are documented in literature. The demonstrated case reveals that increased uptake of FDG in activated neutrophile granulocytes and macrophages has to be taken into consideration in therapy control under chemotherapy, too. In a 53 year old patient FDG-PET was performed after chemotherapy of an abdominal Non-Hodgkin lymphoma for evaluation of persistent tumor vitality. The margin of the persisting mass showed increased uptake of glucose. Histology documented a necrotic center surrounded by granulation tissue.