Sixty-nine patients who underwent transurethral resection of the prostate under subarachnoid anaesthesia were studied. They were randomly allocated to either an early mobilisation group (group A, 30 patients), or a 24 hour bed rest group (group B, 39 patients). The incidence and severity of postspinal headache were assessed in each patient at 24, 48 and 72 hours. The incidence of headache in group B was significantly higher when compared with group A at 48 and 72 hours postoperatively (p less than 0.025 and p less than 0.01, respectively). The total incidence of headache throughout the 72 hours was also significantly higher in group B (p less than 0.01). Regarding the severity of headache the two groups did not differ significantly. Therefore, bed rest is not recommended as a prophylactic measure for postspinal headache.