Background Post-operative cognitive dysfunction (POCD) after non-cardiac surgery is a well known problem in some categories of patients. This study aims to evaluate the influence of auditory evoked potential (AEP)-guided anaesthesia on the requirement for anaesthetic drugs and their influence on POCD. Methods Four hundred and fifty patients aged between 18 and 92 years scheduled for ophthalmic surgery under general anaesthesia were assigned randomly to one of two groups. In group A (AEP group), the depth of anaesthesia (DoA) was aimed at an AEP index (AAI) between 15 and 25. In group C (control group), DoA was guided by clinical signs. Hypotension was treated with fluids and vasopressors using a standardised algorithm. A mini-mental test and the Cognitive Failure Questionnaire were used to evaluate cognitive function. Results Anaesthetic drug requirements were significantly lower in group A than in group C: propofol 92.5 +/- 26.5 vs. 103.8 +/- 39.5 mg (P = andlt;0.001) and desflurane end-tidal concentration 2.5 +/- 0.58 vs. 3.3 +/- 0.79% (P andlt; 0.001). In group A, 36 patients (16%) received additional fluids and vasopressors compared to 65 patients (29%) in group C (P andlt; 0.01). AAI values differed significantly between the groups: 18 (11-21) in group A vs. 12 (10-19) in group C (P andlt; 0.001). The number of patients with POCD was 16 in group C compared to two in group A (P andlt; 0.001) at day 1 post-operation. Conclusion AEP monitoring allows dose reduction of anaesthetic agents, leading to better cardiovascular stability and decreased requirements for intra-operative fluids and vasopressors. Cognitive decline seen following minor ophthalmic surgery, even when anaesthesia is assessed clinically, is short-lived with no long-term sequelae.