The main organs in the left iliac fossa are the descending colon, sigmoid colon and, in women, internal reproductive organs. An infection of the left iliac fossa must lead the clinician firstly to suspect diverticulitis of the sigmoid colon in older patients and salpingitis in women of childbearing age. Other less common aetiologies are possible (inflammatory or infectious colitis, epiploic appendagitis, abscess of the psoas, pyelonephritis, renal abscess, etc.). Sonography as a first-line investigation may lead to diagnosis (especially in gynaecological disease), but a CT scan with intravenous injection of an iodine-containing contrast medium will allow for a full assessment of disease spread, and complications of sigmoid colitis or its differential diagnoses (abscess, fistula, perforation) to be investigated. It can also be used to guide percutaneous drainage or fine-needle aspiration for microbiology investigations.