Cynthia Henry Thielen (born September 22, 1933) is an American politician who served as a member of the Hawaii House of Representatives representing District 50, the Kailua and Kaneohe Bay areas of Oahu County.

She was the Republican nominee for United States Senate in 2006, challenging incumbent Democrat Daniel Akaka.

[12] In her 2018 reelection campaign, she was endorsed by Planned Parenthood's political arm.

[13] In 2013, she was the only Republican in the State House of Hawaii to support same-sex marriage.

Thielen retired from her role as a state legislator, opting not to run in the 2020 general election.