We evaluated the effects of low-dose intrathecal ropivacaine with or without fentanyl for arthroscopic knee surgery. Fifty patients were randomized in equal groups to receive an intrathecal solution (3 ml) containing either 10 mg isobaric ropivacaine or 8 mg isobaric ropivacaine plus 25 pg fentanyl. Complete motor blockade occurred in 22 patients (88%) in both groups. The time taken to reach sensory blockade to T10 and total motor blockade was shorter in the ropivacaine-treated group, but differences were not statistically significant. The duration of sensory and motor blockade was shorter in the ropivacaine plus fentanyl-treated group. The cephalad spread of sensory blockade was higher with ropivacaine than with ropivacaine plus fentanyl. We conclude that although 25 microg fentanyl added to 8 mg ropivacaine provided shorter motor and sensory blockade durations than 10 mg ropivacaine alone, small doses of ropivacaine plus fentanyl can be used safely for arthroscopic knee surgery.