Thalidomide and lenalidomide are structural analogs and immunomodulatory drugs. Lenalidomide appears to have a different safety profile than thalidomide and could be less toxic, and as far as we know, we did not found any study comparing their safety profile. The objective of our study was to review and compare serious adverse drug reactions (SADRs) of thalidomide and lenalidomide spontaneously reported to the French Pharmacovigilance database. We extracted all medically confirmed spontaneous reports of SADR for lenalidomide-based regimens and thalidomide-based regimens from the French Pharmacovigilance database. A "serious" adverse drug reaction (ADR) was defined as an ADR that is fatal or life threatening, which causes hospitalization or prolongation of hospitalization, or permanent or significant disability. The study period was between marketing of 2 drugs and January 15, 2012. A total of 392 SADRs related to thalidomide-based regimens were identified in 244 patients and 377 SADRs related to lenalidomide-based regimens in 220 patients. In spite of their structural analogy, this study highlights interesting differences between lenalidomide and thalidomide's safety profile: nervous system and vascular disorders are more frequent with thalidomide-based regimens while hematologic, skin, infectious disorders and secondary primary cancers are more frequent with lenalidomide-based regimens.