We report a unique case of a patient with synchronous renal cell carcinoma, hepatocellular carcinoma and squamous cell carcinoma of the oral floor. All three tumors were resected during a single operation. The patient was a 75-year-old man with masses in the liver and right kidney discovered by ultrasound examination during a routine checkup. Further examination also revealed a squamous cell carcinoma of the oral floor. The patient underwent a simultaneous radical nephrectomy, enucleation of the liver tumor and resection of the tumor of the oral floor. The diagnoses were histopathologically confirmed. The number of patients with multiple cancers has recently been increasing. The possibility of a second or third malignant lesion should be considered, not only in patients with a known malignancy but also in those without malignancy. The importance of screening procedures in the early detection of malignancy before the appearance of clinical symptoms should be emphasized.