Background: The unspecific non-steroidal anti-inflammatory drug (NSAID) ketorolac is used during surgery as a single dose regimen to reduce immediate postoperative pain. Many studies have shown an increased risk of bleeding in patients treated with NSAIDs. We wanted to investigate whether intraoperative ketorolac administered at the end of surgery resulted in increased bleeding assessed by reduction in haemoglobin and need for blood transfusion. Methods: This was a retrospective review including all patients undergoing laparoscopic Roux-en-Y gastric bypass in the period between January 1st and March 1st, 2010. Haemoglobin levels, time of surgery, fluid treatment and the need for blood transfusion or reoperation were registered. Results: A total of 162 patients were operated in the given period. Of these, the first 47 received intraoperative ketorolac. For the remaining 115 patients, ketorolac was withdrawn. The reduction in haemoglobin in patients receiving intraoperative ketorolac was higher compared with the patients who did not receive ketorolac (-11.3(7.6) % vs. -8.4(6.4) %; p = 0.018). No significant difference was found between the two groups with respect of transfusion requirements (2 out of 47 patients in the ketorolac group versus 0 patients out of 115 in the control group (p = 0.08)). Conclusions: Ketorolac given during surgery may increase the risk of postoperative haemorrhage after laparoscopic Roux-en-Y gastric by-pass.