Background: Recent randomized trials demonstrated that laparoscopic lavage compared with resection for Hinchey III perforated diverticulitis was associated with similar mortality, less stoma formation but a higher rate of early reintervention. The aim of this study was to compare 1-year outcomes in patients who participated in the randomized Scandinavian Diverticulitis (SCANDIV) trial. Methods: Between February 2010 and June 2014, patients from 21 hospitals in Norway and Sweden presenting with suspected perforated diverticulitis were enrolled in a multicentre RCT comparing laparoscopic lavage and sigmoid resection. All patients with perforated diverticulitis confirmed during surgery were included in a modified intention-to-treat analysis of 1-year results. Results: Of 199 enrolled patients, 101 were assigned randomly to laparoscopic lavage and 98 to colonic resection. Perforated diverticulitis was confirmed at the time of surgery in 89 and 83 patients respectively. Within 1 year after surgery, neither severe complications (34 versus 27 per cent; P = 0.323) nor disease-related mortality (12 versus 11 per cent) differed significantly between the lavage and surgery groups. Among the 144 patients with purulent peritonitis, the rate of severe complications (27 per cent (20 of 74) versus 21 per cent (15 of 70) respectively; P = 0.445) and disease-related mortality (8 versus 9 per cent) were similar. Laparoscopic lavage was associated with more deep surgical-site infections (32 versus 13 per cent; P = 0.006) but fewer superficial surgical-site infections (1 versus 17 per cent; P = 0.001). More patients in the lavage group underwent unplanned reoperations (27 versus 10 per cent; P = 0.010). Including stoma reversals, a similar proportion of patients required a secondary operation (28 versus 29 per cent). The stoma rate at 1 year was lower in the lavage group (14 versus 42 per cent in the resection group; P amp;lt; 0.001); however, the Cleveland Global Quality of Life score did not differ between groups. Conclusion: The advantages of laparoscopic lavage should be weighed against the risk of secondary intervention (if sepsis is unresolved). Assessment to excludemalignancy (although uncommon) is advised.