UNLABELLED: The primary aim of this study was to determine the impact of PET in changing initial management plans in patients with untreated head and neck cancer. Secondary aims were to determine the incremental staging information provided by PET and to document the effect of PET on treatment outcomes. METHODS: Patients with untreated head and neck cancer underwent PET scans. Pre-PET management plans were documented by referring clinicians unaware of the PET results, and management plan changes due to PET scan findings were documented. Follow-up to 12 mo after treatment was performed to determine actual management and clinical outcomes. RESULTS: A total of 71 patients (median age, 56 y; 69% male) were studied. PET scans resulted in management change in 33.8% of patients. Moreover, PET was able to detect additional sites of disease in 39.4% of patients. Follow-up data showed that PET improved the classification of patients into curative and palliative categories. Trends toward inferior disease-free survival and lower complete response rates in patients with additional lesions detected on PET were demonstrated. In addition, a trend toward inferior disease-free survival in patients with a higher maximum standardized uptake value was shown. CONCLUSION: These data unequivocally demonstrate the significant impact of PET on management and outcomes in patients with untreated head and neck cancer.