A randomized double-blind trial has shown that, in 160 women with breast cancer undergoing lumpectomy or mastectomy with axillary clearance, perioperative and postoperative administration of tranexamic acid 1 g three times daily resulted in a significant reduction in the mean postoperative drainage volume compared with patients given placebo (283 versus 432 ml, P < 0.001). The frequency of postoperative seroma formation was also decreased by tranexamic acid administration (27 versus 37 per cent, P = 0.2). Haematoma formation was infrequent in both groups and was not altered by administration of tranexamic acid. No infectious complications occurred. Age over 60 years was a significant risk factor for overall wound complications but tumour size and regional lymph node metastases were not. Tranexamic acid may be used to reduce the frequency of postoperative wound complications following surgery for breast cancer.