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BACKGROUND The value of interventions used after acute colonic diverticulitis is unclear. PURPOSE To evaluate postdiverticulitis colonoscopy and interventions to prevent recurrent diverticulitis. DATA SOURCES MEDLINE, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Embase, CINAHL, and ClinicalTrials.gov from 1 January 1990 through 16 November 2020. STUDY SELECTION Comparative studies of interventions of interest reporting critical or important outcomes, and larger single-group studies to evaluate prevalence of colonoscopy findings and harms. DATA EXTRACTION 6 researchers extracted study data and risk of bias. The team assessed strength of evidence. DATA SYNTHESIS 19 studies evaluated colonoscopy. Risk for prevalent colorectal cancer (CRC) compared with the general population is unclear. Based on low-strength evidence, long-term CRC diagnosis is similar with or without colonoscopy. High-strength evidence indicates that risk for prevalent CRC is higher among patients with complicated diverticulitis and colonoscopy complications are rare. Based on high-strength evidence, mesalamine does not reduce recurrence risk (6 randomized controlled trials [RCTs]). Evidence on other nonsurgical interventions is insufficient. For patients with prior complicated or smoldering or frequently recurrent diverticulitis, elective surgery is associated with reduced recurrence (3 studies; high strength). In 19 studies, serious surgical complications were uncommon. LIMITATIONS Few RCTs provided evidence. Heterogeneity of treatment effect was not adequately assessed. CONCLUSION It is unclear whether patients with recent acute diverticulitis are at increased risk for prevalent CRC, but those with complicated diverticulitis are at increased risk. Mesalamine is ineffective in preventing recurrence; other nonsurgical treatments have inadequate evidence. Elective surgery reduces recurrence in patients with prior complicated or smoldering or frequently recurrent diverticulitis, but it is unclear which of these patients may benefit most. PRIMARY FUNDING SOURCE Agency for Healthcare Research and Quality and American College of Physicians. (PROSPERO: CRD42020151246).