Pain following shoulder surgery is reported as severe for 70% of patients, and is a major concern in both hospitalised and ambulatory surgery patients. Pain control is particularly important, as adequate analgesia allows rapid mobilisation of the operated shoulder and prevents complications related to immobility. Several methods have been proposed to treat this pain, the most promising being the interscalene nerve block. The injection of local anesthetics reduces sensation from the shoulder and provides better pain relief after surgery than narcotic medication. To prolong the duration of the analgesia, a catheter must be positioned next to the brachial plexus. Through this catheter, small quantities of local anesthetics can be continuously delivered for several hours after surgery, effectively relieving the worst of the pain.