|Full name||Nelson W. Diebel|
|National team||United States|
|Born||November 9, 1970|
|Height||6 ft 0 in (1.83 m)|
|Weight||185 lb (84 kg)|
|College team||Princeton University|
Nelson W. Diebel (born November 9, 1970) is an American former competition swimmer, Olympic champion, and former world record-holder.
Diebel won two gold medals at the 1992 Summer Olympics in Barcelona, Spain. First, he won the men's 100-meter breaststroke, setting a new Olympic record of 1:01.50 in the event final. Afterward, he swam the breaststroke leg for the winning U.S. team in the men's 4×100-meter medley relay, together with fellow Americans Jeff Rouse (backstroke), Pablo Morales (butterfly) and Jon Olsen (freestyle). In the event final, the four Americans matched the world record of 3:36.93 set by the U.S. team at the 1988 Summer Olympics.
- List of multiple Olympic gold medalists at a single Games
- List of Olympic medalists in swimming (men)
- List of Princeton University Olympians
- List of Princeton University people
- World record progression 4 × 100 metres medley relay