Background: The authors tested the hypotheses that after hip arthroplasty, ambulation distance is increased and the time required to reach three specific readiness-for-discharge criteria is shorter with a 4-day ambulatory continuous lumbar plexus block (cLPB) than with an overnight cLPB. Methods: A cLPB consisting of 0.2% ropivacaine was provided from surgery until the following morning. Patients were then randomly assigned either to continue ropivacaine or to be switched to normal saline. Primary endpoints included (1) time to attain three discharge criteria (adequate analgesia, independence from intravenous analgesics, and ambulation 30 m) and (2) ambulatory distance in 6 min the afternoon after surgery. Patients were discharged with their cLPB and a portable infusion pump, and catheters were removed on the fourth postoperative day. Results: Patients given 4 days of perineural ropivacaine (n = 24) attained all three discharge criteria in a median (25th-75th percentiles) of 29 (24-45) h, compared with 51 (42-73) h for those of the control group (n = 23; estimated ratio = 0.62; 95% confidence interval, 0.45-0.92; P = 0.011). Patients assigned to receive ropivacaine ambulated a median of 34 (9-55) m the afternoon after surgery, compared with 20 (6-46) m for those receiving normal saline (estimated ratio = 1.3; 95% confidence interval, 0.6-3.0; P = 0.42). Three falls occurred in subjects receiving ropivacaine (13%), versus none in subjects receiving normal saline. Conclusions: Compared with an overnight cLPB, a 4-day ambulatory cLPB decreases the time to reach three predefined discharge criteria by an estimated 38% after hip arthroplasty. However, the extended infusion did not increase ambulation distance to a statistically significant degree.