Summary Radiological evidence of inflammation, using computed tomography (CT), is needed to diagnose the first occurrence of diverticulitis. CT is also warranted when the severity of symptoms suggests that perforation or abscesses have occurred. Diverticulitis is classified as complicated or uncomplicated based on CT scan, severity of symptoms and patient history; this classification is used to direct management. Outpatient treatment is recommended in afebrile, clinically stable patients with uncomplicated diverticulitis. For patients with uncomplicated diverticulitis, antibiotics have no proven benefit in reducing the duration of the disease or preventing recurrence, and should only be used selectively. For complicated diverticulitis, non‐operative management, including bowel rest and intravenous antibiotics, is indicated for small abscesses; larger abscesses of 3–5 cm should be drained percutaneously. Patients with peritonitis and sepsis should receive fluid resuscitation, rapid antibiotic administration and urgent surgery. Surgical intervention with either Hartmann procedure or primary anastomosis, with or without diverting loop ileostomy, is indicated for peritonitis or in failure of non‐operative management. Colonoscopy is recommended for all patients with complicated diverticulitis 6 weeks after CT diagnosis of inflammation, and for patients with uncomplicated diverticulitis who have suspicious features on CT scan or who otherwise meet national bowel cancer screening criteria.