Cases of trauma to the conus medularis following spinal anaesthesia have been highlighted recently by Reynolds1. A second report in the same vein described the inaccuracy of using Tuffier's line between the iliac crests to identify a safe lumbar interspace2. As suspected by many clinicians, precise lumbar interspace identification by palpation is prone to error. Broadbent2 et al confirmed this showing that anaesthetists were only 29% accurate, as determined by MRI/ (Ultrasonography was not investigated by Broadbent). The inaccuracy was corroborated by Furness et al3. who showed that clinical identification by anaesthetists using palpation was 30% accurate, as assessed by lumbar spine X-ray. In contrast, in the latter study, placement of markers using ultrasonography at L3-4 interspace was 71% accurate, a figure which is comparable with the 76% accuracy in the preliminary study described below . It should be noted in the Furness study that ultrasonography was performed by a consultant radiologist but in our study an anaesthetist performed the procedure. The Broadbent and Furness studies both documented that identification by anaesthetists using palpation was often inaccurate by two, three or four interspaces. Using ultrasound, in both the Furness3 study and our study, markers were always within one interspace of the intended position.