Diverticulitis should be suspected in patients with isolated left lower quadrant pain, abdominal distention or rigidity, fever, and leukocytosis. Initial laboratory workup includes a complete blood count, basic metabolic panel, urinalysis, and C-reactive protein measurement. Computed tomography with intravenous contrast is the preferred imaging modality, if needed to confirm diagnosis and assess for complications of diverticulitis. Treatment decisions are based on the categorization of disease as complicated vs. uncomplicated. Selected patients with uncomplicated diverticulitis may be treated without antibiotics. Complicated diverticulitis is treated in the hospital with modified diet or bowel rest, antibiotics, and pain control. Abscesses that are 3 cm or larger should be treated with percutaneous drainage. Emergent surgery is reserved for when percutaneous drainage fails or the patient's clinical condition worsens despite adequate therapy. Colonoscopy should not be performed during the flare-up, but should be considered six weeks after resolution of symptoms in patients with complicated diverticulitis who have not had a high-quality colonoscopy in the past year. Diverticulitis prevention measures include consuming a vegetarian diet or high-quality diet (high in fruits, vegetables, whole grains, and legumes), limiting red meat and sweets, achieving or maintaining a body mass index of 18 to 25 kg per m², being physically active, and avoiding tobacco and long-term nonsteroidal anti-inflammatory drugs. Partial colectomy is not routinely recommended for diverticulitis prevention and should be reserved for patients with more than three recurrences or abscess formation requiring percutaneous drainage.