Background: The development of laparoscopic and robotic surgeries represents the modern era with the objective of improving patient outcomes; this surgical method is widespread in urology and general surgery. Retroperitoneal laparoscopic/robotic surgery is common in urologic surgery, but not in liver surgery. Tumors located in the posterosuperior aspect of the liver are difficult to access using a transperitoneal approach, and control of bleeding can also be difficult, especially in patients with cirrhosis. Case Presentation: Herein, we present a 66-year-old man who had a cirrhotic liver with concurrent renal and hepatic tumors. The renal tumor was located at the upper pole of the right kidney and the liver tumor was located at the liver dome (segment VII); the patient underwent simultaneous robotic hepatectomy and partial nephrectomy with a retroperitoneal approach. Conclusion: To our knowledge, this is the first case involving a retroperitoneal approach for a simultaneous robotic hepatectomy and partial nephrectomy; this method was feasible and safe. We hope this approach serves as an alternative surgical method for patients with synchronous renal and posterior segment liver tumors.