Yoda, the world’s oldest mouse, celebrated his fourth birthday on Saturday, April 10, 2004. A dwarf mouse, Yoda lives in quiet seclusion with his cage mate, Princess Leia, in a pathogen-free rest home for geriatric mice belonging to Richard A. Miller, M.D., Ph.D., a professor of pathology in the Geriatrics Center of the University of Michigan Medical School. Yoda was born on April 10, 2000 at the U-M Medical School. At 1,462-days-old, Yoda is now the equivalent of about 136 in human-years. The life span of the average laboratory mouse is slightly over two years.