Background: The Revised International Staging System (R-ISS) has recently been introduced as a comprehensive prognostic score for multiple myeloma (MM). Validation of the R-ISS in patients treated outside of clinical trials is the focus of current investigations. The aim of this study was to test the prognostic role of the R-ISS in MM patients ineligible for autologous stem cell transplantation. Patients and Methods: A total of 102 newly diagnosed MM patients were analyzed. All patients were initially treated with thalidomide-based combinations. Results: An overall response rate was achieved in 77.4% patients. Both the International Staging System (ISS) and the R-ISS influenced the event-free survival and the overall survival (OS). However, the ISS was unable to discriminate patients in stages ISS1 and ISS2 regarding OS. On the contrary, the R-ISS clearly differentiated risk categories regarding OS and provided an improved discriminative power of 6.3% compared to the ISS. Furthermore, among the parameters that were significant in univariate analysis (presence of renal impairment, anemia, platelet count < 130 × 109/l, and R-ISS), the multivariate model pointed to the R-ISS (p = 0.001) as the most important parameter influencing OS. Conclusion: The R-ISS represents a useful tool for risk stratification of transplant-ineligible MM patients and should be considered as a prognostic index in daily clinical practice.