A retrospective study by questionnaire was carried out on 3056 patients (1457 female and 1599 male patients) to ascertain morbidity after spinal anaesthesia with 0,5% isobaric bupivacaine, with special regard taken to the incidence of post spinal headache. It was found that in female patients below the age of 50 the incidence of complaints was higher than in male patients, especially in the 30-50 year range. In male patients the incidence was higher in the 40-60 year group, with the highest incidence in the 50-60 year olds. The size of needle employed played a definite role. The complaints distributed according to the site of operation showed a dependence on age and size of needle. Altogether, 324 post spinal headaches were detected, 194 (13.3%) in female patients, significantly more than the 130 (8.1%) reported by male patients. In patients over 60, the incidence dropped and there was no sex difference. There was a higher incidence of headache with larger needles used for spinal anaesthesia. 84% the headaches cleared up within 2 weeks. Only in 9% did the headache persist longer than 4 weeks.