Intra-operative awareness can lead to serious adverse psychological consequences. We conducted a prospective, randomised, double-blinded trial in 920 patients undergoing breast cancer surgery under bispectral index-guided total intravenous anaesthesia to evaluate the effect of penehyclidine hydrochloride on intra-operative awareness. Patients were randomly divided to receive 0.01−1 penehyclidine hydrochloride or saline intravenously 30 min before surgery. The pre-administration, pre-operative anxiety levels were assessed using a 100-mm visual analogue scale. Intra-operative awareness was defined as recall of intra-operative events using a modified Brice interview administered 2–6 h postoperatively, and in the next 24–48 h. A committee of three experts, blinded to the study conditions, independently scrutinised all reported recollections. We found no differences in depth of anaesthesia and patients' pre-operative anxiety levels between the two groups. The incidence of awareness with penehyclidine hydrochloride (0/456 patients; 0%) was significantly lower than with saline (5/452; 1.1%), p = 0.030. We conclude that penehyclidine hydrochloride reduced the incidence of intra-operative awareness in patients undergoing breast cancer surgery during general anaesthesia.