Diethelm may refer to:
Surnames Barbara Diethelm (born 1962), Swiss painter Caspar Diethelm (1926–1997), Swiss composer Hans Diethelm (born 1967), Swiss former skier Michael Diethelm (born 1985), Swiss footballer Pascal Diethelm (born 1944), Swiss anti-tobacco activist Rolf Diethelm (born 1940), Swiss former ice hockey player
First names Diethelm Ferner (born 1941), German football coach Diethelm Sack (born 1948), German businessman Diethelm von Eichel-Streiber (1914–1996), German Luftwaffe pilot
Middle names Heidi Diethelm Gerber (born 1969), Swiss sport shooter
See also 24858 Diethelm, an asteroid named after Swiss astronomer Roger Diethelm