An exploratory study was undertaken to determine the precision with which an anaesthetist could identify the correct L3-4 interspace using ultrasonography. Twenty-three ultrasonographic examinations of lumbar spine were performed by an anaesthetic senior house officer with minimal training on patients undergoing an elective MRI scan of the lumbar spine. Seventeen patients were eligible for inclusion in this study. Patients' median age was 47 years, and body mass index 27 kg/m2. In 13 of the 17 (76%) patients, the SHO using ultrasonography was able to place a marker correctly at the L3-4 interspace as indicated by MRI. In four patients, the marker was at the L2-3 interspace. In five of the 17 patients apposition of spinous processes was noted on MRI scan and it was in three of these patients that the marker was at the L2-3 interspace.