PURPOSE: This study was performed to find the applicable equations which determine the proper needle depth for lumbar puncture in Korean pediatric patients using spine magnetic resonance imaging(MRI). METHODS: The authors enrolled the patients who had spine MRI from August 2007 to June 2008 and were aged less than 20 years. Eighty eight patients whose height(Ht.) and weight(Wt.) were recorded within 10 days from spine MRI were recruited. The posterior dural depths and dural widths were measured on each L2-3, L3-4, and L4-5 levels of intervertebral space. By comparing the R squares, the most significant independent variables for posterior dural depth were selected, and by calculating malposition rate, the further insertion distance from posterior dural depth and the final puncture depth equation were determined. RESULTS: The proper puncture depths with the lowest malposition rate were as follows. L2-3 puncture depth (mm) = 126.5xWt./Ht. (kg/cm)+7.1 or 0.613xWt. (kg)+16.1 L3-4 puncture depth (mm) = 136.0xWt./Ht. (kg/cm)+7.6 or 0.656xWt. (kg)+17.3 L4-5 puncture depth (mm) = 138.3xWt./Ht. (kg/cm)+7.5 or 0.665xWt. (kg)+17.5 CONCLUSION: Lumbar puncture depth is best predicted using weight and height as independent variables. And the equations of each tap sites were different in constants. Using this formula, the rate of failure and complication in lumbar can be diminished, but it should be validated by further studies.