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. A Republican, she served in the state House of Representatives from 1990 until 2020. She served as minority floor leader from 1992 to 1997 and was the assistant minority leader at the time of her retirement. She was the Republican nominee for United States Senate in 2006, challenging incumbent Democrat Daniel Akaka. She lost to Akaka, 62% to 38%, in the general election.