In this study the histopathological features of an underestimated architectural variety of infiltrating squamous cell carcinoma of the larynx and hypopharynx, operationally termed as "superficial extending carcinoma", are described. Pathologically, the superficial extending carcinoma is a poorly/moderately differentiated infiltrating squamous cell carcinoma showing an entirely or predominant superficial type of growth; deep infiltration was confined to the mucosa or limited to a few underlying glandular and/or muscular laryngopharyngeal structures, regardless of the presence of lymph node metastasis or lymph vessel invasion. As defined above, the superficial extending carcinoma may be regarded, from a pathologic point of view, as a laryngopharyngeal counterpart to "superficial esophageal carcinoma". Studying a series of 88 whole organs serially sectioned laryngopharyngectomy specimens, we found that 6 out of 61 primary laryngeal carcinomas (9.8%) and 6 out of 26 primary hypopharyngeal carcinomas (23%) showed the peculiar architectural features of the superficial extending carcinoma. In 6 cases (2 laryngeal and 4 hypopharyngeal) the tumor was entirely intramucosal or early infiltrated the underlying muscle or gland structures. In the remaining 6 cases (4 laryngeal and 2 hypopharyngeal tumor) a superficial extending carcinoma was found to be associated with a deeply infiltrating squamous cell carcinoma of the "classic" type. Features useful to histopathologic diagnosis of superficial extending carcinoma and to its differentiation from preneoplastic and other neoplastic lesions of the laryngopharyngeal mucosa are emphasized. The possible association of superficial extending carcinoma with multiple synchronous and metachronous neoplastic lesions in the upper aerodigestive tract and the frequent underestimation of its real extension may have important clinical implications.