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The aim of this study was investigate the appearance of multiple myeloma on flurorine--18 fluorodeoxyglucose positron emission tomography (FDG-PET). Furthermore the accuracy of FDG-PET in detecting myeloma lesions and its influence on patient's management were evaluated.Altogether 50 patients, 13 patients with newly diagnosed multiple myeloma with negative radiographs, 4 patients with solitary plasmocytoma, 27 patients in remission with suspected relapse and 6 patients with monoclonal gammopathy of unknown significance (MGUS) with suspicion for multiple myeloma or other malignancy underwent FDG-PET examination. The results of routinely performed radiographs, and MR or CT imaging modalities as well as the clinical course were used for verification of the FDG-PET results.Focally increased tracer uptake was observed in 3 (23 %) of newly diagnosed myeloma patients with negative radiographs and was verified with CT or MR with followed indication for therapy. The FDG-PET was negative in two cases of newly diagnosed multiple myeloma with negative radiographs, no focal infiltration on MR imagination, but with anemia, high monoclonal imunoglobulin and bone marrow infiltration, which was indication for therapy. In all other cases FDG-PET negativity in asymptomatic myeloma had good prognostic significance; these patients are without progression after with a median follow up 14 (7-20) months. Focally increased tracer uptake was found in 5 of the 27 patients in remission. In 4 cases of them it was due to multiple myeloma relapse, in one case due to ovarial carcinoma. Only in 1 patient the PET-FDP failed to recognize extraosseal progression on the scull. 21 patients had true negative FDG-PET imagination, in 1 case disease relapsed 12 months after FDG-PET examination; the other 20 patients are still without progress of this disease with median follow up 15 (7-20) months. FDG-PET was positive in 2 from the 6 patients with MGUS. In one of them carcinoma of thyreoidea was detected, in second the FDG-PET activity was localized in gut, tumor was verified with CT and colonoscopy.In conclusion, FDG PET might contribute to initial staging of radiographs negative multiple myeloma and might be useful for follow up of patients in remission, especially in consecratory multiple myeloma, or in patients with large plasmocelular tumor (5 cm) after concomitant radiochemotherapy.