Background:The aim of the present study is to present the three years follow-up a randomised controlled trial that compared Hartmann's Procedure (HP) with sigmoidectomy with primary anastomosis (with or without defunctioning ileostomy) (PA) in a randomised design to determine the optimal treatment strategy for perforated diverticulitis with purulent or fecal peritonitis. Methods: Data were prospectively gathered for the first 12 months after randomization and retrospectively collected up to 36 months. The primary long-term endpoint was stoma free rate 36 months after the index procedure. Secondary outcomes were patients with a stoma at 36 months, percentage of stoma reversals, related reinterventions, parastomal/incisional hernia rates, total in hospital days including all readmissions regardless their relation to the intervention, overall morbidity and mortality. Results: Three years follow-up was completed in 119 of the originally 130 included patients, with 57 (48%) in the PA-group and 62 (52%) patients in the HP-group. 36 months stoma free rate was significantly better for patients undergoing PA compared with HP (PA 92% vs HP 81%, hazard ratio 2.326 [95% CI 1.538-3.517]; log-rank p < 0⋅0001). Stoma reversal rates did not significantly differ (PA 31/40(78%) versus HP 45/61(74%), p = 0.814). Overall cumulative morbidity (PA 21/57(36%) versus HP 30/62(48%), p = 0.266) and mortality (PA 6/57(11%) versus HP 7/62 (11%), p = 1.000) did not differ between groups. However, more parastomal hernias occurred in the HP-group (HP 10/62(16%) vs PA 1/57(2%), p = 0.009) and the mean total in hospital days after three years follow-up was significantly lower in the PA-group compared to the HP-group (PA 14 days (IQR 9.5-22.5) versus HP 17 days (IQR 12.5-27.5)), p = 0.025). Conclusion: Long-term results showed that in haemodynamically stable, immunocompetent patients primary anastomosis is superior to Hartmann's procedure as treatment for perforated diverticulitis with respect to longterm stoma free rate, overall hospitalization and parastomal hernias.