Objective: The prognosis of multiple myeloma (MM) patients is highly heterogeneous. The aim of this study is to determine the impact of patients’ renal functions on the prognostic performance of the International Staging System (ISS). In addition, we aimed to evaluate the results of survival of patients with ISS stages and normal renal functions and those with ISS stages and abnormal renal functions with this study. Materials and Methods: Two hundred and four patients with newly diagnosed MM who received an autologous stem cell transplantation after induction chemotherapy in our tertiary care center between the years of 2001 and 2018 were evaluated. Results: There were 153 (75%) MM patients who had a glomerular filtration rate (GFR) of ≥60 mL/min and 51 (25%) MM patients who had GFR of <60 mL/min at the time of diagnosis in this study. There was a strong correlation between ISS stage and GFR. The ISS stages were higher in patients who had GFR of <60 mL/min than patients who had GFR of ≥60 mL/min (p<0.001). Patients with GFR of <60 mL/min were significantly more prevalent in the ISS III group than ISS I and II (p<0.001). Conclusion: This study showed that the ISS provides significant prognostic information in MM patients with GFR of ≥60 mL/min at diagnosis. However, in patients with impaired renal function at the time of diagnosis, B2-microglobulin may not be a good prognostic indicator since it may be affected by renal dysfunction as well as tumor burden.