The purpose of this study was to identify the patient position for lumbar puncture associated with the widest interspinous distance utilizing ultrasound. Sixteen healthy adult volunteers were placed in three positions commonly used for lumbar puncture (lateral recumbent with knees to chest, sitting and bent forward over an adjustable bedside stand, and sitting with feet supported and chest to knees) and the distance between lumbar spinous processes was measured by ultrasound. Measurements were compared between the three positions. Differences were analyzed using Tukey's honestly significant difference test. The results showed that the interspinous distance was significantly greater in the "sitting, feet supported" position than in the other two positions ( P<0.001). The "sitting, feet supported" position may offer advantages for selected patients undergoing lumbar puncture. Ultrasonography may be a useful adjunct when performing lumbar puncture in the emergency department.