BACKGROUND: We have studied the influence of aging on the spread of analgesia and blood pressure with 0.5% hyperbaric bupivacaine in elderly patients compared to findings with a control group. METHODS: Forty-nine patients in two groups between 22-59 yr and 70-86 yr undergoing lower limb surgery were placed in a lateral position with the side to be operated on dependent. Five minutes after the injection of 1.4 ml of 0.5% hyperbaric bupivacaine, each patient was placed in the surgical position. Noninvasive mean arterial pressure (MAP) and levels of analgesia were measured for 30 minutes. RESULTS: The maximum sensory block level was T7.5+/-2.4 in the elderly group and T8.2+/-2.4 in the control group. There was no significant difference on the highest level of analgesia between groups. The time to reach maximum level was 17.4+/-8.6 minutes in the elderly group and 16.9+/-7.0 minutes in the control group. The maximum decrease in MAP was significantly greater in the elderly group (23.3+/-11.1% of the baseline value) than in the control group (10.7+/-0.2%). The incidence of hypotension (defined as a decrease of 25% or more MAP) was 48.0% in the elderly group and 4.2% in the control group. CONCLUSIONS: There was no significant effect on the highest level of analgesia with advancing age. Decreases in mean arterial pressure were more frequent and pronounced in the elderly group than in control group. It may be appropriate to monitor patients carefully and treat hypotension immediately if it occurs.