Post-dural-puncture headache (PDPH) is a complication of puncture of the dura mater (one of the membranes that surround the brain and spinal cord). It is a common side-effect of spinal anesthesia and lumbar puncture and may occasionally accidentally occur in epidural anesthesia. Leakage of cerebrospinal fluid through the dura mater puncture causes reduced fluid levels in the brain and spinal cord, and may lead to the development of PDPH hours or days later. Onset occurs within two days in 66 percent and within three days in ninety percent of PDPH cases. It occurs so rarely immediately after puncture that other possible causes should be investigated when it does.