Solitary caecal diverticulitis is a rare and often misdiagnosed cause of abdominal pain. A 63-year-old Caucasian woman was admitted with a 3-day history of left upper quadrant pain and constipation. Preoperative imaging identified a possible transverse colonic tumour. At laparotomy a long, mobile ascending colon resulted in the caecal pole lying in the left upper quadrant and an inflamed gangrenous solitary caecal diverticulum was found. A right hemicolectomy was performed and the patient recovered promptly.