Among 873 consecutive patients who had undergone a total of 1021 spinal anaesthesias involving puncture of the lumbar dura, 75 (7.35%) complained of Postdural Puncture Headache (PDPH). The severity of each patient's PDPH was categorized, on a scale from mild to severe, on the basis of the onset, duration, severity of the headaches, and the degree to which they were accompanied by auditory and vestibular symptoms. In the patients who developed PDPH, 65% developed symptoms within 24 hours of the lumbar punctures and 92% developed symptoms within 48 hours. For the patients who recovered spontaneously the mean duration of the PDPHs was 5 days, with a range of 1-12 dyas. PDPH was characterized by headaches that were influenced by the patient's posture and the severity of PDPH was categorized as follows: Mild PDPH resulted in a slight restriction of their physical activity. These patients were not confined to bed and had no associated symptoms. Moderate PDPH forced the patient to stay in bed for part of the day, and resulted in restricted physical activity. Associated symptoms were not necessarily present. Severe PDPH. Patients were bedridden for the entire day and made no attempt to raise their head or to stand. Associated symptoms were always present. Forty-five of the PDPH patients (60%) recovered spontaneously. Of these, 8 patients (11%) were categorized as mild cases of PDPH, 14 (19%) as moderate, and 23 (30%) patients as severe cases of PDPH. Thirty of the PDPH patients (40%) were treated with an autologous epidural blood patch (AEBP). Of these, 27 patients (36%) were classified as severe and 3 patients (4%) as moderate PDPH.(ABSTRACT TRUNCATED AT 250 WORDS)