The anatomy of the lumbar plexus and the various approaches used to perform lumbar plexus blockade are reviewed. A single needle technique for a posterior approach to the plexus at the L2-3 interspace is described. This technique was used bilaterally in six intact cadavers, and the extent of spread of an injected dye was documented photographically during a subsequent detailed dissection of the region. In all cases, dye was confined to the posterior part of the psoas muscle, and tracked down the nerves of the lumbar plexus. No dye was seen anterior to the psoas, around the sympathetic chain, on the sacral plexus or in the extradural or subarachnoid spaces. Further studies in patients with needle position and drug disposition being confirmed using computerised tomography and X ray scanning were in agreement with the results observed in the cadavers. This technique represents a simple approach to the lumbar plexus which does not require needle localisation by X ray screening.