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Background: Little is known about patients with appendicitis presenting at nighttime. It is hypothesized that patients presented at night more frequently have a complicated (gangrenous or perforated) appendicitis and therefore develop more postoperative complications. Methods: In this study data were used from the nationwide, prospective SNAPSHOT study appendicitis, including 1975 patients undergoing surgery for suspected appendicitis. This study included only adults. Two primary outcomes were defined: (A) The proportion of patients with complicated appendicitis and (B) the proportion of patients with a complication postoperatively presenting during daytime versus nighttime period. Analysis for both complicated and uncomplicated appendicitis was performed, and a multivariate model was used to correct for baseline characteristics and time to surgery. Results: In total, 1361 adult patients with appendicitis were analyzed. Both at nighttime and at daytime, 34% had complicated appendicitis. In patients presenting in the daytime, 12.1% developed a postoperative complication versus 18.6% for presentation at night (p = 0.008). In a multivariate analysis, the risk for a postoperative complication when presenting at night was significantly increased (adjusted OR 1.74; 95% CI 1.14–2.66, p = 0.01). Surgery within eight hours after presentation does not lower this risk (adjusted OR 1.37; 95% CI 0.97–1.95, p = 0.078). Conclusion: Complicated appendicitis is seen as frequently during the day as at nighttime. For patients who present at nighttime with acute appendicitis, the risk of a postoperative complication is higher compared with a presentation at daytime. In multivariate analysis, nighttime presentation but not surgery within 8 h after presentation is independently associated with postoperative complication risk.