Severe complications following colonoscopy are rare. This is a case report of a 44-year-old woman, who presented to an emergency department (ED) 24 hours following an uncomplicated colonoscopy performed in an out-patient clinic. Acute contrast-enhanced CT (CECT) was performed, showing acute appendicitis, which was later confirmed by a laparoscopy and histology. Weeks prior, the patient had been admitted to the ED with lower abdominal pain. On this occasion, CECT was performed, showing acute inflammation of the sigmoid colon.