BACKGROUND Extranodal NK/T cell lymphoma is a rare tumour, typically involving the upper aerodigestive tract. Even rarer is primary extranasal disease involving the skin, testis, soft tissue and gastrointestinal tract. METHODS We report a case of a 46-year-old Chinese male who presented with six months history of abdominal pain, weight loss and rectal bleeding. Diagnostic colonoscopy revealed multiple aphthous ulcers within the ileo-caecal region and distal transverse colon, separated by normal mucosa, mimicking skip lesions of Crohn's colitis. Computer topography (CT) scan of the abdomen showed multiple circumferential thickenings involving predominantly the right colon. A clinical diagnosis of colonic Crohn's disease with possible perforation was made. An extended right hemicolectomy was performed due to uncontrolled rectal bleeding. Histopathology examination of the colon showed infiltration by malignant lymphoid cells associated with necrosis, angiocentricity and angiodestruction. Immunohistochemical studies confirmed T-cell monoclonality, presence of cytotoxic granules and Epstein-Barr virus (EBV) infection. A diagnosis of extranodal NK/T cell lymphoma of the colon was made. CONCLUSIONS These findings highlight that colonic NK/T cell lymphoma may clinically mimic other benign inflammatory lesions and should be one of the differential diagnoses in patients presenting with gastrointestinal lesions. The final diagnosis is only possible with appropriate histological and immunohistochemical studies.