UNLABELLED We present a case of a negative positron emission tomography (PET) scan in a patient with pathologic viable cancer at neck dissection. STUDY DESIGN Case Report. METHODS A 69-year-old man presented with clinical stage T2N2c squamous cell cancer of the left tonsil and was treated with definitive chemoradiation. Left-sided adenopathy decreased but remained palpable after therapy. RESULTS PET scan performed 23 days after completion of treatment showed no suspicious uptake in the left neck. Neck dissection performed at 2 months post-therapy revealed viable tumor in left cervical nodes. CONCLUSIONS Persistent adenopathy after chemoradiation for head and neck cancer remains a clinical dilemma. A negative PET scan is accurate but only if the scan is performed 3 to 4 months after therapy.