Two hundred and ten patients, 145 males and 65 females, aged 20 to 72 years old, ready to receive extracorporeal shock wave lithotripsy under epidural anesthesia were studied to evaluate if any correlation existed between body weight, body surface area, body mass index and body height and the depth to the epidural space. The mean value for the depth to the epidural space was 4.77 +/- 0.55 cm for males, 4.25 +/- 0.55 cm for females and the overall average was 4.61 +/- 0.60 cm. The range of the depth to the epidural space was 3.0-7.0 cm. Linear regression analysis revealed significant correlation between body weight, body surface area, body mass index, body height an the depth to the epidural space, in the order of BW greater than BSA greater than BMI greater than BH. It is concluded that body weight, body surface area, body mass index and body height affect the depth to the epidural space and play an important role in predicting the depth to the epidural space.