Background Total knee arthroplasty (TKA) is associated with intense post‐operative pain. Besides providing optimal analgesia, reduction in side effects and enhanced mobilization are important in this elderly population. The adductor‐canal‐blockade is theoretically an almost pure sensory blockade. We hypothesized that the adductor‐canal‐blockade may reduce morphine consumption (primary endpoint), improve pain relief, enhance early ambulation ability, and reduce side effects (secondary endpoints) after TKA compared with placebo. Methods Patients aged 50–85 years scheduled for TKA were included in this parallel double‐blind, placebo‐controlled randomized trial. The patients were allocated to receive a continuous adductor‐canal‐blockade with intermittent boluses via a catheter with either ropivacaine 0.75% (n = 34) or placebo (n = 37) (http://www.clinicaltrials.gov Identifier: NCT01104883). Results Seventy‐five patients were randomized in a 1 : 1 ratio and 71 patients were analyzed. Morphine consumption from 0 to 24 h was significantly reduced in the ropivacaine group compared with the placebo group (40 ± 21 vs. 56 ± 26 mg, P = 0.006). Pain was significantly reduced in the ropivacaine group during 45 degrees flexion of the knee (P = 0.01), but not at rest (P = 0.06). Patients in the ropivacaine group performed the ambulation test, the Timed‐Up‐and‐Go (TUG) test, at 24 h significantly faster than patients in the placebo group (36 ± 17 vs. 50 ± 29 s, P = 0.03). Conclusion The adductor‐canal‐blockade significantly reduced morphine consumption and pain during 45 degrees flexion of the knee compared with placebo. In addition, the adductor‐canal‐blockade significantly enhanced ambulation ability assessed by the TUG test.