Ethisterone (pregneninolone, 17α-ethynyltestosterone or 19–norandrostane) is a progestin. It is the 17α-ethynyl analog of testosterone, and was synthesized in 1938 by Hans Herloff Inhoffen, Willy Logemann, Walter Hohlweg, and Arthur Serini at Schering AG in Berlin and marketed in Germany in 1939 as Proluton C and by Schering in the U.S. in 1945 as Pranone. It was the first orally-active progestin.

Ethisterone was also marketed in the U.S. from the 1950s into the 1960s under a variety of trade names by other pharmaceutical companies that had been members of the pre-World War II European hormone cartel (Ciba, Organon, Roussel).

Ethisterone is made by the ethynylation of androstenolone with acetylene and successive oxidation of the hydroxyl group at C₃ of the steroid system.