BACKGROUND: Several local anaesthetic techniques are available for cataract surgery. Recently, topical anaesthesia has gained in popularity. A randomized trial was designed to compare patient discomfort and intraoperative complications following routine cataract surgery under topical or sub-Tenon's anaesthesia. METHODS: A randomized double-blinded placebo-controlled clinical trial of 210 patients assigned to either a sub-Tenon's group (sub-Tenon's anaesthesia with placebo topical balanced salt solution, n=140) or a topical anaesthesia group (topical anaesthesia with placebo sub-Tenon's injection of balanced salt solution, n=70) was carried out. All patients underwent phacoemulsification with intraocular lens implantation. Patients in the sub-Tenon's group received a single injection (3 ml) of a combination of lidocaine 2% (2 ml) and bupivacaine 0.75% (1 ml), and four doses of topical placebo (balanced salt solution). Patients in the topical anaesthesia group received four doses of topical proxymethocaine 0.5% and a placebo sub-Tenon's injection (3 ml) of balanced salt solution. No intracameral injection of local anaesthetic was given. A 10-point visual analogue pain scale was used preoperatively and for postoperative pain assessment immediately after the operation and 30 min postoperatively. The intraoperative complications in the two groups were recorded. RESULTS: The mean pain score immediately after surgery was 2.42 (sd 2.2) in the sub-Tenon's group and 3.44 (2.3) in the topical anaesthesia group (P=0.0043). The mean pain score 30 min after surgery was 1.24 (1.7) in the sub-Tenon's group and 2.25 (2.2) in the topical anaesthesia group (P=0.0009). CONCLUSIONS: Patients undergoing cataract surgery under topical anaesthesia experience more postoperative discomfort than patients receiving sub-Tenon's anaesthesia. Surgery-related complications were similar in both groups.