Primary T/natural killer (NK) cell lymphoma of the colon is extremely rare. Despite the advances in histological and immunophenotypic studies, the diagnosis of primary T/NK cell lymphoma of the colon can be delayed because the early symptoms and colonoscopic findings may be very similar to those of inflammatory bowel diseases such an Crohn's colitis, and most physicians have little available information on this group of neoplasms. Moreover, florid nonspecific inflammatory infiltrates would not allow characterization of the tumor cells in such an inflammatory background. Herein, we describe a patient who initially presented with features that were clinically and colonoscopically similar to Crohn's colitis. Three months later, he had cecal bleeding and perforation, and primary T/NK cell lymphoma of the colon was diagnosed through immunophenotypic and genotypic studies of surgical specimens.