IMPORTANCE: Diverticulitis is a common disease. Recent changes in understanding its natural history have substantially modified treatment paradigms. OBJECTIVE: To review the etiology and natural history of diverticulitis and recent changes in treatment guidelines. EVIDENCE REVIEW: We searched the MEDLINE and Cochrane databases for English-language articles pertaining to diagnosis and management of diverticulitis published between January 1, 2000, and March 31, 2013. Search terms applied to 4 thematic topics: pathophysiology, natural history, medical management, and indications for surgery. We excluded small case series and articles based on data accrued prior to 2000. We hand searched the bibliographies of included studies, yielding a total of 186 articles for full review. We graded the level of evidence and classified recommendations by size of treatment effect, according to the guidelines from the American Heart Association Task Force on Practice Guidelines. FINDINGS: Eighty articles met criteria for analysis. The pathophysiology of diverticulitis is associated with altered gut motility, increased luminal pressure, and a disordered colonic microenvironment. Several studies examined histologic commonalities with inflammatory bowel disease and irritable bowel syndrome but were focused on associative rather than causal pathways. The natural history of uncomplicated diverticulitis is often benign. For example, in a cohort study of 2366 of 3165 patients hospitalized for acute diverticulitis and followed up for 8.9 years, only 13.3% of patients had a recurrence and 3.9%, a second recurrence. In contrast to what was previously thought, the risk of septic peritonitis is reduced and not increased with each recurrence. Patient-reported outcomes studies show 20% to 35% of patients managed nonoperatively progress to chronic abdominal pain compared with 5% to 25% of patients treated operatively. Randomized trials and cohort studies have shown that antibiotics and fiber were not as beneficial as previously thought and that mesalamine might be useful. Surgical therapy for chronic disease is not always warranted. CONCLUSIONS AND RELEVANCE: Recent studies demonstrate a lesser role for aggressive antibiotic or surgical intervention for chronic or recurrent diverticulitis than was previously thought necessary. Copyright 2014 American Medical Association. All rights reserved.