A 17-year-old white male patient was referred to the otolaryngology clinic with a 6-month history of a left-sided neck mass. His primary care physician initially obtained an ultrasonographic image, which demonstrated a left, level 2 lymph node measuring 4.0 × 1.5 × 2.8 cm. The patient then underwent several courses of antibiotic treatment, but the mass persisted. After a period of conservative management, he developed a sore throat and fever. He subsequently underwent a computed tomographic scan of the neck and chest with contrast, which demonstrated an isolated, enlarged, homogenously enhancing left-neck level 2B lymph node measuring 3.4 × 2.8 × 2.1 cm (Figure 1A). When he presented to our facility, he was found to have an asymptomatically enlarged left level 2/5A neck mass that was nontender and fixed. The patient had an unremarkable medical, surgical, and social history and no known infectious exposures. A white blood cell count and C-reactive protein level were both elevated, at 11 310 cells/μL (to convert to cells × 10 9 per liter, multiply by 0.001) and 56.2 mg/L (to convert to nanomoles per liter, multiply by 9.524), respectively. Studies for influenza A and B, HIV, cytomegalovirus, American foulbrood, Bartonella henselae, infectious mononucleosis, and Epstein-Barr virus had negative results. An ultrasonographyguided needle biopsy was performed. Fine-needle aspiration and flow cytometry had negative results for lymphoproliferative disorders or a malignant condition. A tissue culture had negative results. Given the inconclusive diagnosis, the patient underwent a left neck dissection of levels 2A, 2B, and 5A. Intraoperative frozen sections did not show a malignant process. On final analysis, a pathologic examination of the largest lymph node was performed (Figure 1B). Diagnosis D. Castleman disease DiscussionCastleman disease (CD) is an uncommon, lymphoproliferative dis-