Background: Total hip arthroplasty (THA) is a common procedure associated with moderate postoperative pain. No nerve block without loss of motor function has been documented for THA. We hypothesised that an ultrasoundguided lateral femoral cutaneous nerve (LFCN) block added to a multimodal postoperative pain regimen would reduce postoperative pain after THA. Methods: One hundred patients who had a THA by the posterior approach were evaluated in this randomised, placebo-controlled, blinded, parallel-group trial comparing an ultrasound-guided LFCN-block with either 8 ml of ropivacaine, 7.5 mg/ml, (Group Ropivacaine) or 8 ml of saline (Group Placebo) given postoperatively. Surgery was performed under spinal anaesthesia. The primary outcome was pain (measured on a Visual Analogue Scale (VAS)) 4 h post-blockade during 30� flexion of the hip. Secondary outcomes were pain at rest, pain during movement, oxycodone consumption (0-24 h), time to mobilisation, ability to mobilise, and length of stay. Patients, assessors and all staffinvolved with patient care were blinded to the intervention. Results: There was no difference in primary outcome between Group Ropivacaine and Group Placebo (VAS 27 mm vs. 31 mm, p = 0.41; difference -5 mm (95 % CI: -15 mm - +5 mm). No differences in any of the secondary outcomes were observed. No adverse events, or harms, were observed during the trial. Conclusion: Pain scores, opioid use, time to mobilisation, and length of stay were low in both Group Ropivacaine and Group Placebo. We found no added analgesic effect of a LFCN-block when combined with paracetamol and ibuprofen after THA by the posterior approach.