Amyloidoisis in patients with Waldenström macroglobulinemia (WM) mostly involves the heart, peripheral nerves and kidneys. Retroperitoneal amyloidosis is a rare finding. We describe a 62-year-old man with an incidental finding of a monoclonal gammopathy and elevated inflammatory parameters. Bilateral moderately active retroperitoneal infiltration with punctiform calcifications was found on fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) imaging. Taken together, these findings are suggestive of Waldenström associated amyloidosis. Computed tomography-guided retroperitoneal biopsy confirmed the diagnosis.