Anaesthetists use dexamethasone principally for its anti-emetic effect. The purpose of this study was to characterize the effects of a single intraoperative dose of dexamethasone on cellular and metabolic components of the immune system in patients undergoing laparoscopic surgical procedures. Methods. In this prospective double-blind trial, female patients undergoing elective major laparoscopic surgery were randomized to receive saline (Control group, n16) or dexamethasone 4mg (Dexamethasone group, n16) i.v. after the induction of anaesthesia. Inflammatory markers and immune cell counts were examined at 24 and 48h and 6 weeks after surgery. The changes from baseline preoperative values were compared between groups using a Mann-Whitney U-test, and linear mixed models were used to validate the findings. Results. No differences in concentrations of serum glucose and interleukin-6 were observed between groups after surgery. The increase in C-reactive protein concentration at 24h after surgery was greater in the control group [median (interquartile range), 33 (25-65) vs 17 (7-26)mg dl1; P0.018]. Extensive changes in the counts of white cells, including most lymphocyte subsets, were observed 24h after surgery, and dexamethasone appeared to attenuate most of these changes. Changes at 48h and 6 weeks did not differ between groups. Conclusions. In female patients undergoing elective laparoscopic gynaecological surgery, dexamethasone administrationappears to attenuate inflammation and to alter immune cell counts at 24 h, with no effects identified after this time. The importance of these changes for postoperative immune function is unknown. Trial registration. Australia and New Zealand Clinical Trials Registry (ACTRN12608000340336).