82 unilateral total knee arthroplasty patients (ASA physical status I-III) were randomized into four groups: a pre-treatment group with femoral nerve bock (FNB) after spinal anesthesia but before operation, a post treatment group with FNB immediately after operation, a pre-control group with sham FNB before operation, and post-control group with sham FNB after operation. After 72 hours follow up, FNB groups consumed less morphine and had better visual analogue scores over the first 24 hours regardless of time of FNB timing compared to sham groups. However, no differences were found between pre and post-operative FNB groups in morphine consumption, or maximum flexion range on day 2 and 3.