Abstract Purpose : This study evaluated the prognostic role of 18F-FDG PET/CT at baseline in patients with newly diagnosed multiple myeloa (MM) and evaluated the prognostic relevance of 18F-FDG PET/CT for each stage according to the Revised International Staging System (R-ISS). Method: We retrospectively analyzed the records of 167 patients with newly diagnosed MM. 18F-FDG PET/CT was performed prior to induction therapy in patients with newly diagnosed MM. A Focal lesions (FL) at diagnosis was defined as focally increased FDG uptake greater than the physiologic bone marrow or liver uptake, with or without any underlying lesion. Extramedullary disease (EMD) was defined as FDG-avid soft tissue that was not contiguous to bone. Results: A total of 102 patients (61.1%) had at least one FL at diagnosis, and 44.9% had more than three FLs. EMD was present in 13.2% of all patients. In the total cohort, the presence of more than three hypermetabolic FLs or EMD on baseline PET/CT was associated with significantly inferior progression free survival (PFS) and overall survival (OS) than other patients. Because most patients (91%) with EMD had more than three FLs, PET/CT positivity was defined as the presence of more than three FLs or the presence of EMD. The C-reactive protein level was higher (0.550 vs. 0.245 mg/L, P = 0.004) and the serum albumin level was lower in the PET/CT-positive group (3.5 vs. 3.6 g/dL, P = 0.040). Patients who were PET/CT-positive had a significantly lower complete response rate after first-line therapy compared with those who were PET/CT-negative (15.6% vs. 34.4%, P = 0.007). In multivariate analyses, PET/CT positivity was an independent predictor of PFS and OS in all patients. Fifty-five patients (46.1%) with R-ISS II were PET/CT-positive at baseline and had significantly shorter PFS and OS. PET/CT positivity was also correlated with poor PFS and OS in patients with R-ISS III. Conclusion : 18F-FDG PET/CT was an independent predictor of survival outcomes in patients with newly diagnosed MM. In addition, performing 18F- FDG PET/CT at diagnosis may be useful for determining the survival outcomes of MM patients with R-ISS II and III. Figure. Figure. Disclosures No relevant conflicts of interest to declare.