Primary adenosquamous carcinomas of the intestine are rare, particularly in the small intestine. One case, in the jejunum of an adult female, is described here. The patient was a 70-year-old Japanese woman presenting with upper abdominal pain. Computed tomography of the abdomen showed a mass in the small intestine, measuring 86 x 44 mm, and a double-contrast barium study revealed a filling defect in the upper jejunum. The patient was diagnosed as suffering from upper small-intestinal cancer, and surgical excision was performed. Histological examination, including immunohistochemistry and electron microscopy, revealed the tumor to have both malignant glandular and squamous components. A review of the literature regarding this type of lesion is presented.