Background Examinations used to search for unknown primary tumors of squamous cell carcinomas of the neck include CT, MRI, laryngoscopy, gastrointestinal endoscopy, and positron‐emission tomography (PET). Narrow band imaging (NBI) endoscopy in which an optical color‐separation filter is used to narrow the bandwidth of spectral transmittance is also used. Methods Twenty‐eight patients in whom primary squamous cell carcinomas could not be detected with conventional white light laryngoscopy underwent NBI endoscopy and PET. Results Primary lesions were detected with NBI endoscopy in 3 patients, but no primary lesions were detected with PET. However, PET was used to detect a lower gingival cancer and a palatine tonsillar cancer. Conclusion Both PET and NBI endoscopy is effective for detecting unknown primary tumors of squamous cell carcinomas of the neck. © 2011 Wiley Periodicals, Inc. Head Neck, 2011