Acute diverticulitis (AD) results from inflammation of a colonic diverticulum. It is the most common cause of acute left lower-quadrant pain in adults and represents a common reason for acute hospitalization, as it affects over half of the population over 65 years with a prevalence that increases with age. Although 85% of colonic diverticulitis will recover with a nonoperative treatment, some patients may have complications such as abscesses, fistulas, obstruction, and /or perforation at presentation. For these reasons, different classifications were introduced through times to help clinicians to develop a correct diagnosis and guide the treatment and for the same reasons imaging is used in most cases both to realise a differential diagnosis and to guide the therapeutic management. US and CT are both usefull in diagnosis of diverticolitis, and their sensibility and specificity are similar. However CT scanning is essential for investigating complicated diverticular disease especially where there are diffuse signs and clinical suspicion of secondary peritonitis; instead in most uncomplicated cases the experienced sonographer may quickly confirm a diagnosis guided by the clinical signs. US is to be recommended in premenopausal women, and in young people to reduce dose exposure.