Abstract Background Wound infection remains a common and serious complication after colonic surgery. Although many colonic operations are performed laparoscopically, it remains unclear whether this has any impact on the incidence of wound infection. Subcutaneous tissue oxygenation is an excellent predictor of surgical wound infection. The impact of open and laparoscopic colonic surgery on tissue oxygenation was compared. Methods Fifty-two patients undergoing elective open and laparoscopic left-sided colonic resections were evaluated in a prospective observational study. Anaesthesia management was standardized and intraoperative arterial partial pressure of oxygen was kept at 150 mmHg in both groups. Oxygen tension was measured in the subcutaneous tissue of the right upper arm. Results At the start of surgery subcutaneous tissue oxygen tension (Psqo2) was similar in both groups (mean(s.d.) 65·8(17·2) and 63·7(23·6) mmHg for open and laparoscopic operations respectively; P = 0·714). Tissue oxygen remained stable in the open group, but dropped significantly in the laparoscopic group during the course of surgery (Psqo2 after operation 53·4(12·9) and 45·5(11·6) mmHg, respectively; P = 0·012). Conclusion Laparoscopic colonic surgery significantly decreases Psqo2, an effect that occurs early in the course of surgery. As tissue oxygen tension is a predictor of wound infection, these results may explain why the risk of wound infection after laparoscopic surgery remains higher than expected.