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Key Clinical Message: Rituximab‐induced serum sickness (RISS) is a rare complication of Rituximab (RTX) in immunobullous disorders. Clinicians should be aware of the occurrence of serum sickness symptoms during RTX administration, and prompt initiation of corticosteroid therapy is crucial in these patients. Additionally, RISS may occur with subsequent RTX doses and patients should be counseled accordingly. Rituximab (RTX) is a chimeric monoclonal anti‐CD20 antibody which has gained approval for the treatment of various autoimmune and lymphoproliferative disorders. While RTX‐induced minor reactions, including immediate infusion‐related reactions, are common, serum sickness is rare. Limited data exist regarding rituximab‐induced serum sickness (RISS) in pemphigus vulgaris (PV) and mucous membrane pemphigoid (MMP). We report two cases of RISS following RTX administration in PV and MMP patients. Both patients presented with typical symptoms of serum sickness after RTX infusion, necessitating drug cessation and corticosteroid therapy for resolution. RISS represents a rare complication of RTX therapy. Clinicians should maintain awareness of serum sickness presentations during and post‐RTX administration. [ABSTRACT FROM AUTHOR]