We report a case of Burkitt lymphoma with largely extranodal disease localizations at staging. Chemotherapy was given, thus obtaining a complete metabolic response in all previous disease sites as shown at a control PET, however associated to the appearance of new focal uptake areas in the liver; these findings were confirmed at US and MRI. Chemotherapy determined also neutropenia that was treated by filgrastim, followed by a prompt and important medullary response. Liver biopsy revealed extramedullary hematopoiesis, probably filgrastim induced. Filgrastim administration may cause false-positive findings in the liver at FDG PET.