To investigate the effect of a restricted intravenous fluid regimen versus a standard regimen on complications after colorectal resection. Current fluid administration in major surgery causes a weight increase of 3-6 kg. Complications after colorectal surgery are reported in up to 68% of patients. Associations between postoperative weight gain and poor survival as well as fluid overload and complications have been shown. We did a randomized observer-blinded multicenter trial. After informed consent was obtained, 172 patients were allocated to either a restricted or a standard intraoperative and postoperative intravenous fluid regimen. The restricted regimen aimed at maintaining preoperative body weight; the standard regimen resembled everyday practice. The primary outcome measures were complications; the secondary measures were death and adverse effects. The restricted intravenous fluid regimen significantly reduced postoperative complications both by intention-to-treat (33% versus 51%, P = 0.013) and per-protocol (30% versus 56%, P = 0.003) analyses. The numbers of both cardiopulmonary (7% versus 24%, P = 0.007) and tissue-healing complications (16% versus 31%, P = 0.04) were significantly reduced. No patients died in the restricted group compared with 4 deaths in the standard group (0% versus 4.7%, P = 0.12). No harmful adverse effects were observed. The restricted perioperative intravenous fluid regimen aiming at unchanged body weight reduces complications after elective colorectal resection.