Objective: Lenalidomide is an effective immunomodulatory derivative drug used in the treatment of multiple myeloma (MM). It is available in original and generic forms in Turkey, but there is no clinical study that has compared the effectiveness and adverse events (AEs) of the generic and original forms of lenalidomide. We compared the effectivity and AEs of generic and original lenalidomide in patients with relapsed/refractory MM (RRMM). Materials and Methods: Patients with RRMM using original or generic lenalidomide were evaluated retrospectively. Overall response (OR), complete response (CR), very good partial response (VGPR), partial response (PR), stable disease, and progressive disease rates and hematologic and nonhematologic AEs were evaluated in these RRMM patients. The results were described as numbers, frequencies, and percentages and were analyzed using PASW 19.0 for Windows with chi-square and Fisher exact tests. Results: The number of patients using original lenalidomide was 55 and the number of patients using generic lenalidomide was 43. The OR rate was 67.2% for patients using original lenalidomide and 60.4% for those on generic lenalidomide. CR and VGPR rates were 14.5% and 45.4% in the original group while the CR and VGPR rates were 20.9% and 18.6%, respectively, in patients using generic lenalidomide. Hematologic AEs were similar in the two groups while some nonhematologic AEs were less common in the original lenalidomide group than the generic group. Only pyrexia as a grade 3-4 AE was more common in the original lenalidomide than the generic lenalidomide group. Conclusion: This study showed that the generic form of lenalidomide has similar efficacy with the original form of lenalidomide in the treatment of RRMM. The AEs of original lenalidomide were generally fewer than those of generic lenalidomide. Further studies involving a larger number of patients with RRMM would be useful for comparing the efficacy and AEs of original and generic lenalidomide.