Objective Hartmann's procedure (HP) still remains the most frequently performed procedure in acute perforated diverticulitis, but it results in a end colostomy. Primary anastomosis (PA) with or without defunctioning loop ileostomy (DI) seems a good alternative. The aim of this study was to assess differences in the rate of stomal reversal after HP and PA with DI and to evaluate factors associated with postreversal morbidity in patients operated for acute perforated diverticulitis.Method All 158 patients who had survived emergency surgery for acute perforated diverticulitis in five teaching hospitals in The Netherlands between 1995 and 2005 and underwent HP or PA with DI were retrospectively studied. Age, gender, ASA-classification, severity of primary disease, delay of stoma reversal, surgeon's experience, surgical procedure and type of anastomosis were analysed in relation to outcome after stoma reversal.Results Of the 158 patients, 139 had undergone HP and 19 PA with DI. The reversal-rate was higher in patients with DI (14 ⁄ 19; 74%) compared to HP (63 ⁄ 139; 45%) (P = 0.027) Delay between primary surgery and stoma reversal was shorter after PA with DI compared with HP (3.9 vs 9.1 months; P < 0.001). Cumulative postreversal morbidity after HP was 44%. Early surgical complications occurred in 22 of 63 patients. Morbidity after DI reversal was 15% (P < 0.001). Three patients died after HP reversal, none died after DI reversal. Anastomotic leakage was observed in 10 patients after HP reversal. This was less frequently observed when the operation was performed by a specialist colorectal surgeon (10% vs 33%; P = 0.049) and when a stapled anastomosis was performed (4% vs 24%; P = 0.037).Conclusions Reversal of HP should only be performed by an experienced colorectal surgeon, preferably performing a stapled anastomosis, or probably not be performed at all, as it is accompanied by high postoperative morbidity and even mortality. It is important that these findings are taken in account for when performing primary emergency surgery for acute perforated diverticulitis.