We evaluated the effect of low-dose bupivacaine plus fentanyl administered intrathecally in elderly patients undergoing transurethral prostatectomy. Patients were randomly assigned to one of two groups. Group F received plain bupivacaine 4 mg with 25 micro g of fentanyl and sterile water to a total of 1.5 ml, and Group B received only 0.5% plain bupivacaine 7.5 mg for spinal anaesthesia. Sensory block was adequate for surgery in all patients. The mean level of motor block was higher and the duration of motor block was longer in Group B (p < 0.0001). Hypotension and shivering were significantly more common in Group B (p < 0.05). The addition of fentanyl 25 micro g to plain bupivacaine 4 mg provides adequate analgesia for transurethral prostatectomy with fewer side-effects in elderly patients when compared with the conventional dose of bupivacaine.