Rituximab, a monoclonal antibody directed against the CD20 antigen on B lymphocytes, is commonly used in the treatment of hematologic malignancies and rheumatologic disorders.<sup>1,2</sup> It acts to rapidly deplete the B lymphocyte population through multiple mechanisms, leading to dysregulation of the immune system.<sup>3</sup> Rituximab has been associated with numerous adverse gastrointestinal effects including diarrhea and bowel perforation, and recent reports have associated rituximab with the development of de novo inflammatory bowel disease (IBD).<sup>4,5</sup> To our knowledge, there have been no reports of microscopic colitis (MC) associated with rituximab therapy.