We report 13 patients with oral and maxillofacial cancers and upper digestive tract cancers detected using GIF. The site of the primary oral lesion was most frequently the oral floor in 4 of 13 cases. However, it is difficult to draw conclusions regarding any tendency about the primary oral lesion site in double cancer. Histology of oral and maxillofacial cancer and esophageal cancer was squamous cell carcinoma in all cases, while that of gastric cancer was adenocarcinoma in 4 cases and anaplastic carcinoma in 1 case. We detected double cancer synchronously in 10 cases, but metachronously in 3 cases. The incidence of double cancer in patients with smoking and drinking habits was 6.695 times higher than that in patients without smoking and/or drinking habits (logistic regression analysis). Almost all lesions in the upper digestive tract were detected in the early stage; therefore we treated the oral and maxillofacial cancers prior to treating the secondary cancers. A radical treatment protocol was developed for 10 cases and 8 of these 10 cases were successfully treated. However, some cases demonstrated progression during the treatment of oral and maxillofacial cancers. Based on our experience with such poor outcomes, we recommend treating oral and maxillofacial cancer accurately and promptly, and establishing a close relationship between oral and maxillofacial surgeons and doctors treating the upper digestive tract. It is also important to consider ways to simultaneously treat both lesions in double cancer.