Positron emission tomography (PET) is a relatively new radiologic imaging technique based on glucose analog uptake and metabolism in tumor tissue. In this study, PET was used in evaluating 38 patients with laryngeal cancer. Twenty-five patients were examined with PET prior to treatment to study the reliability of PET in identifying the primary tumor and assessing regional nodal status; 13 patients who had previously received irradiation with curative intent and who represented differential diagnostic problems were imaged to differentiate between irradiation effects and recurrent or residual cancer. Findings for both groups were compared to results of clinical evaluation and those of computed tomography (CT) and magnetic resonance imaging (MRI). The PET results were essentially identical to those of CT, MRI, and clinical evaluation in identifying metastatic lesions (82% correct), and were as reliable as CT and MRI for correctly identifying primary tumors (88%). Positron emission tomography was most helpful in differentiating recurrent tumor from postirradiation tissue sequelae. However, its lack of anatomic detail made PET less valuable for primary staging and therapeutic planning. It may enhance the diagnostic accuracy of CT and MRI where anatomic distortions occur or where diagnostic criteria for CT and MRI are ambiguous.