Acute calcific retropharyngeal tendinitis is an underrecognized cause of pain and stiffness in the neck associated with odynophagia and retropharyngeal soft-tissue swelling. We report on five patients in whom an initial misdiagnosis of this entity as a retropharyngeal or nasopharyngeal abscess, a neoplasm, or a fracture-dislocation of the cervical spine led to interventions such as admission to the hospital and parenteral administration of antibiotics. An open biopsy was performed in one patient because of a suspected neoplasm. Evaluation of the tissue specimen with routine and polarized light microscopy, scanning electron microscopy, and energy-dispersive spectrometry demonstrated a foreign-body inflammatory response to deposited crystals of hydroxyapatite. In all five patients, the correct diagnosis was established only after retrospective review of the radiographic studies by a physician who was familiar with acute calcific retropharyngeal tendinitis. The computed tomographic findings of acute calcific retropharyngeal tendinitis are distinctive and consist of prevertebral calcification localized to the insertion of an edematous tendon of the longus colli muscle. Symptomatic relief was provided with anti-inflammatory and analgesic medications. The symptoms resolved, without sequelae, within one to two weeks for all of the patients. We hope that an increased awareness of hydroxyapatite deposition in the tendon of the longus colli muscle will result in improved early diagnosis of acute calcific retropharyngeal tendinitis.