BACKGROUND: The duration of spinal anesthesia depends upon two factors; concentration of local anesthetics in the CSF and vascular absorption of the local anesthetics. However, there are some arguments on the relationship between the maximum block level and the duration of the block in spinal anesthesia. METHODS: Fifty seven patients scheduled for surgery on a lower limb or perineum underwent spinal anesthesia with 11 mg of 0.5% hyperbaric bupivacaine. After confirming final block heights (T12-T3, range), we took two study groups, group I (block height > OR = T6, n = 30) and group II (block height < OR = T9, n = 27). We checked the maximal sensory block level, the time to maximal sensory block level, a two-segment regression time, the duration of sensory block to T12, and L5 during the first 30 minutes at 2.5 minute intervals and then, at 30 minutes intervals. Blood pressure and pulse rate were measured in the same time interval. RESULTS: The maximal sensory block level and the time to maximal sensory block level of group I was T5.0, 14.6 minutes and that of group II were T9.7, 11.4 minutes. The mean cephalad spread of analgesia in group I was more rapidly increased at 20 minutes and there were statistically significant differences between the two groups from 5 min to 110 minutes. The duration of sensory block to T12, L5 was similar in group I and II. No significant differences in blood pressure and pulse rate were found between the two groups. CONCLUSIONS: We found that there was no relationship between the sensory block level and duration of the block in spinal anesthesia using a fixed does of local anesthetic.