PET-Fluorodeoxyglucose scanning is an imaging test based on the increased uptake of radiolabelled glucose by tumour cells. PET might detect neck tumours better than other imaging tests. This is a cohort study in which patients with N2 N3 squamous cell carcinoma of the head and neck undergo a PET and a CT scan at baseline and then post-radiation therapy and chemotherapy. Then, they undergo neck dissection surgery. The PET and CT results are compared with the presence or absence of tumours in the neck nodes. If PET is sufficiently accurate in predicting the presence or absence of tumours in the neck nodes, then a neck dissection could be avoided.