Rosai and Dorfman first described sinus histiocytosis with massive lymphadenopathy (SHML) in 1969 with an article detailing 4 cases in which they differentiated this disease entity from the grouping of diseases categorized as histiocytosis X, where it was previously classified. Also known as Rosai-Dorfman disease (RDD), it is clinically characterized as massive, painless, bilateral, symmetric cervical lymphadenopathy, with fever and leukocytosis. An 11-year-old African American boy was referred to our clinic for extraction of a severely decayed tooth #30 and evaluation of a large right-sided neck mass. Initially, the patient had been seen by his general dentist who had diagnosed the mass as an odontogenic abscess. After 2 courses of different antibiotics, no changes in the mass were noted. Subsequently, the patient was sent to the emergency department where CT revealed multiple right-sided neck masses with the largest measuring 4 × 2 cm. The patient underwent an incisional biopsy by otolaryngology and a diagnosis of necrotic lymph tissue was made. Upon our examination, the carious tooth #30 was felt to be an incidental finding and fine-needle aspiration cytology of the largest mass was performed in 2 places. This also provided a diagnosis of necrotic lymph tissue. In concert with the patient and his mother, the decision was made to excise the mass because of psychosocial concerns. A massive right-sided lymph node attached to the submandibular gland was found and excised without complication. Histologic examination with S-100 stain confirmed a diagnosis of RDD. The patient healed well following surgery and has experienced no further lymphadenopathy. This case presentation and review of the literature is unique, as the patient presented with unilateral cervical lymphadenopathy only. Open biopsy and 2 fine-needle aspirations all returned as necrotic lymph tissue. Obtaining the correct diagnosis was additionally hampered by coincidental dental pathology on the affected side and final diagnosis was made only by excisional biopsy, which is not necessarily indicated in cases of RDD. Copyright © 2011 Mosby, Inc. All rights reserved.