Introduction. During periacetabular osteotomy (PAO), the sciatic, femoral, and obturator nerves are at risk. Most frequently nerve lesions can be attributed to a mechanical cause; however, in the absence of a clear mechanical cause surgeons are faced with a diagnostic problem and in many cases no diagnosis will be established. We report a case of inflammatory neuropathy of the lumbosacral plexus following a PAO. Case Presentation. A 31-year-old female developed weakness of ankle and knee flexion and extension 6 months after a PAO. Electrophysiological studies revealed damage to the obturator, femoral, and sciatic nerve consistent with an inflammatory lumbosacral plexopathy. MRI of the lumbosacral plexus was normal. The patient was treated with multimodal pain therapy and prolonged physiotherapy; nevertheless, symptoms worsened over time. At 2-year follow-up, there were no signs of recovery. Discussion. Inflammatory neuropathy of the lumbosacral plexus is a potential cause of pain and weakness after ipsilateral orthopaedic procedures. It should be distinguished from more frequently encountered mechanical causes of postsurgical neuropathy based on clinical suspicion, electrophysiological studies, MRI, and nerve biopsy. It is important that the orthopaedic community is aware of this complication since there is some evidence that early recognition and initiation of immunosuppressive therapy can lead to improved clinical outcome.