A prospective, blind, randomised trial was undertaken to determine if the incidence of postlumbar puncture headache is significantly altered by 24 hours' recumbency. One hundred and two patients were allocated randomly to rest supine in bed for either 4 or 24 hours after spinal anaesthesia for urological or gynaecological surgery. A standardised spinal anaesthetic technique was applied that incorporated the use of a 22-gauge needle. All patients were followed-up prospectively to determine if there was a difference in the incidence of postlumbar puncture headache between the two groups. Five patients (11.6%) who were recumbent for 4 hours developed postlumbar puncture headache, a result which was not statistically significantly different from the seven patients (11.9%) in the other group who complained of postlumbar puncture headache.