Abstract <p>Recently, with the increasing number of injections in the lying ear, various complications have emerged. We present a case report of vestibular dysfunction in a 39-year-old woman following hyaluronic acid injection into the ear, a relatively uncommon complication associated with this procedure. The patient exhibited symptoms such as nausea, vomiting, tongue hemiplegia, nystagmus, and gait instability immediately after the injection at the cranioauricular sulcus. Prompt administration of hyaluronidase into the sulcus anthelicis transversus and cranioauricular sulcus did not alleviate the symptoms. Subsequently, the patient required hospital admission in a wheelchair the following day. After a thorough examination and consultations with neurology and otolaryngology specialists, the patient was diagnosed with acute unilateral vestibular disease. Subsequent to comprehensive treatment focused on vestibular decompression, the patient experienced significant alleviation of symptoms and regained the ability to walk independently. The underlying mechanism of the lesion involved the accumulation of a substantial amount of hyaluronic acid in the mastoid region via the facial nerve canal, leading to its entry into the inner ear due to gravitational and pressure forces, causing vestibular dysfunction and symptoms such as vertigo, nausea, and walking instability. Understanding the anatomy in the injection area is helpful to diagnose and manage the related complications.</p> Level of Evidence IV <p>This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors <a href="http://www.springer.com/00266">www.springer.com/00266</a>.</p>