Abstract The number of ambulatory surgical procedures is increasing throughout the world. This is partly due to the development of a number of new anaesthetic, analgesic and adjuvant drugs, each with more rapid onset and shorter duration of action, over the past two decades. An interest in the issues discussed in this thesis arose out a desire to improve the quality of anaesthesia for patients who undergo day-case surgery. A second aim was to compare the different anaesthetic methods in terms of recovery from anaesthesia and costs. A total of 233 patients undergoing day-case knee arthroscopy under either 2% or 5% lidocaine spinal anaesthesia or general anaesthesia with desflurane, isoflurane, propofol or sevoflurane were investigated in two prospective, randomised clinical trials. The overall aims were to find the most suitable, satisfactory and economically feasible method for adult ambulatory knee arthroscopy and to assess the factors that affect the immediate postoperative period and the one-week recovery profile at home. The patients were highly satisfied with all the methods of anaesthesia. There was a slight tendency in favour of general anaesthesia compared to spinal anaesthesia. The general level of pain after ambulatory knee surgery was low after the first few hours postoperatively and continued to be low during the first postoperative week. After short-acting general anaesthesia with desflurane, isoflurane and propofol, home readiness was achieved over two hours earlier than after 5% lidocaine spinal anaesthesia. Home readiness was significantly delayed after 2% lidocaine spinal anaesthesia compared to sevoflurane inhalation anaesthesia. General anaesthesia with isoflurane was cheaper than the other general anaesthetics, i.e. desflurane, sevoflurane, propofol, or 2% and 5% lidocaine spinal anaesthesias. Propofol anaesthesia was the most expensive. The spinal anaesthesia patients had a higher incidence of headache, backache and lower leg pain during the first postoperative week than the patients who had had general anaesthesia. In busy ambulatory surgery units, remarkable savings may be achieved by using short-acting general anaesthetics, i.e. desflurane and isoflurane, instead of propofol or sevoflurane general anaesthesias or lidocaine spinal anaesthesia. This is due to the lower costs of desflurane and isoflurane compared to sevoflurane and propofol and the shorter time needed for postoperative care compared to spinal anaesthesia.