Cervical lymphadenopathy in adults has a broad differential diagnosis, including bacterial and viral infections, Kikuchi-Fujimoto disease, systemic lupus erythematosus, and various neoplasms. Many of its etiologies share similar symptomatology and presentations, which complicates the diagnosis. A thorough history and a comprehensive physical examination, to include nasopharyngoscopy and imaging as indicated by the specific case, are key to determining the origin of the lymphadenopathy and to avoid a missed or delayed diagnosis. Based on our review of the literature, we present the second reported case of anaplastic lymphoma kinase-positive anaplastic large-cell lymphoma presenting in an adult with an obstructing adenoid/nasopharyngeal mass and lymphadenopathy. The mass, which occurred in a 19-year-old woman of Asian descent, caused nasal airway obstruction in the setting of cervical lymphadenopathy that was initially ascribed to mononucleosis.