OBJECTIVE: To evaluate whether mandatory imaging is an effective strategy in suspected appendicitis for reducing unnecessary surgery and costs. METHODS: In 2010, guidelines were implemented in The Netherlands recommending the mandatory use of preoperative imaging to confirm/refute clinically suspected appendicitis. This retrospective study included 1,556 consecutive patients with clinically suspected appendicitis in 2008-2009 (756 patients/group I) and 2011-2012 (800 patients/group II). Imaging use (none/US/CT and/or MRI) was recorded. Additional parameters were: complications, medical costs, surgical and histopathological findings. The primary study endpoint was the number of unnecessary surgeries before and after guideline implementation. RESULTS: After clinical examination by a surgeon, 509/756 patients in group I and 540/800 patients in group II were still suspected of having appendicitis. In group I, 58.5% received preoperative imaging (42% US/12.8% CT/3.7% both), compared with 98.7% after the guidelines (61.6% US/4.4% CT/ 32.6% both). The percentage of unnecessary surgeries before the guidelines was 22.9%. After implementation, it dropped significantly to 6.2% (p<0.001). The surgical complication rate dropped from 19.9% to 14.2%. The average cost-per-patient decreased by 594 <euro> from 2,482 to 1,888 <euro> (CL:-1081; -143). CONCLUSION: Increased use of imaging in the diagnostic work-up of patients with clinically suspected appendicitis reduced the rate of negative appendectomies, surgical complications and costs. KEY POINTS: * The 2010 Dutch guidelines recommend mandatory imaging in the work-up of appendicitis. * This led to a considerable increase in the use of preoperative imaging. * Mandatory imaging led to reduction in unnecessary surgeries and surgical complications. * Use of mandatory imaging seems to reduce health care costs.