Neutropenic enterocolitis (typhlitis) is an unusual acute complication of neutropenia, most often associated with leukaemia and lymphoma and characterized by segmental caecal and ascending colonic ulceration that may progress to necrosis, perforation, and septicaemia. We present a unique case of an 8-year-old girl with recently diagnosed infectious mononucleosis having findings consistent with typhlitis on abdominal CT.