Background: Transient femoral nerve palsy (TFNP) is a well-known complication associated with ilioinguinal-iliohypogastric nerve block (IINB). We compared the incidence of TFNP after ultrasound-guided IINB and that after anatomical landmark-based IINB. Methods: We reviewed medical records of adult patients (ASA-PS 1-3, Age 21-87) who had received inguinal hernia surgery under general anesthesia and IINB retrospectively. IINB was performed using 0.5% ropivacaine either by ultrasound-guidance (US group, n=16) or by landmark-based technique (LM group, n=17). TFNP was defined as sensory loss in the anterior aspect of the thigh or weakness of quadriceps femoris muscle in the nerve-blocked side. Results: The frequency of TFNP in US group (6%) was lower than that in LM group (41%) in the postanesthesia care unit (P=0.019). TFNP symptom was resolved completely on the morning after surgery. The incidence of severe-intermediate postoperative pain and analgesic requirement were not different between the two groups Conclusions: This study revealed that ultrasound-guided technique is effective to lower the incidence of TFNP after IINB in adult inguinal hernia surgery.