The incidence of postdural puncture headache (PDPH) was investigated prospectively in 873 consecutive patients undergoing a total of 1021 spinal anesthesias, and its association to age, sex, needle size, number of attempted dural punctures, needle bevel direction, duration of postoperative recumbency, and previous PDPH was analyzed. Multivariate analysis showed that age (P less than 0.0001), direction of the bevel of the needle when puncturing the dura mater (P = 0.022), and a history of previous PDPH (P = 0.018) were significant predictors of PDPH. The estimated relation between PDPH, on the one hand, and age and orientation of the bevel, on the other, enables the anesthetist to predict the risk of PDPH and thereby to choose an acceptable age limit for spinal anesthesia.