CHARLES SUMNER, R-MA
1851–1874
Missed more than three years—from May 1856 through December 1859—after being attacked with a cane by Rep. Preston Brooks (D-SC) on the Senate floor.
 

CARTER GLASS, D-VA
1920–1946
Took a leave of absence due to heart problems in 1942. His seat remained empty until his death in 1946.
 

LYNDON B. JOHNSON, D-TX
1949–1961
Had a heart attack in 1955 and took five months to recover.
 

KARL MUNDT, R-SD
1948–1973
Suffered a stroke in 1969 and was largely absent for the rest of his term.
 

JOE BIDEN, D-DE
1973–2009
Had surgery for two aneurysms in 1988 and was out for seven months.
 

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Photography: (Glass) Library of Congress, Prints and Photographs Division; (Mundt) Bettmann/Corbis/AP Images; (Biden) Nancy Stone/Chicago Tribune