The first case of mucosal spreading adenocarcinoma at the hilum of the lung is presented. The patient was a 72 year old Japanese male smoker. The carcinoma was located at the right main bronchus with involvement of the apical, posterior and anterior segmental bronchi. The tumor consisted of stratified oval or polygonal cells and signet ring cells spreading along the bronchial mucosa in an in situ fashion with extension down the bronchial gland ducts and acini. Only a small micro-invasive focus not extending beyond the bronchial cartilage was seen. Immunohistochemically, the tumor was positive for lysozyme but negative for lactoferrin and PE-10 indicating that this tumor was possibly showing goblet cell differentiation.