Ultrasound guidance allows real-time identification of relevant anatomy and needle position when performing brachial plexus regional anaesthesia. The aim of this investigation was to determine whether the use of surface ultrasound could improve the quality of brachial plexus anaesthesia for upper limb surgery. Forty patients were randomized to either conventional "landmark-based" plexus anaesthesia, or to an ultrasound-guided approach using a 13 mHz linear array transducer Both interscalene and axillary techniques were used. The use of ultrasound significantly improved the onset and completeness of sensory (P=0.011) and motor (P=0.002) block. Ultrasound guidance also significantly reduced (P=0.012) the incidence of paraesthesia during the performance of the blocks. Ultrasound guidance increases the quality of sensory and motor blockade in brachial plexus regional anaesthesia, and by reducing the incidence of paraesthesia during performance of the blocks, may confer greater safety.