Orthognathic surgery can cause substantial bleeding. Recent meta-analyses concluded that there is a statistically significant reduction in perioperative blood loss with the preventive use of tranexamic acid (TA). However, the mean reported difference in bleeding was moderate, and the clinical relevance of this blood-sparing effect remains debated. We therefore conducted a prospective, double-blind, randomized, placebo-controlled equivalence study of the effect of TA in patients undergoing Lefort I or bimaxillary osteotomies. Our main outcome measure was total blood loss on postoperative day 1. The equivalence margin was ± 250 ml for the difference in blood loss and its 95% confidence interval. One hundred and forty-seven patients were randomized, of which 122 underwent bimaxillary osteotomies. Blood loss in the treatment group was 682 ± 323 vs. 875 ± 492 ml. The mean difference in bleeding was -132 [-243; -21] ml as per-protocol, but -193 [-329; -57] ml in intention-to-treat: the limits of this confidence interval exceeded the margin of equivalence. Similar results were obtained when analysing only patients undergoing bimaxillary osteotomy. Haemoglobin decreased by 1.8 ± 1.2 g/dl with TA, vs. 2.6 ± 1.1 g/dl with placebo (p<0.001). Our study did not demonstrate equivalence between TA and placebo on perioperative blood loss in orthognathic surgery. TA may reduce blood loss but without evidence of clinical consequences.