The American College of Physicians (ACP) developed this guideline to provide clinical recommendations on the role of colonoscopy for diagnostic evaluation of colorectal cancer (CRC) after a presumed diagnosis of acute left-sided colonic diverticulitis and on the role of pharmacologic, nonpharmacologic, and elective surgical interventions to prevent recurrence after initial treatment of acute complicated and uncomplicated left-sided colonic diverticulitis. This guideline is based on the current best available evidence about benefits and harms, taken in the context of costs and patient values and preferences.