This episode reviews the evidence for the prenatal estrogen theory of being transgender in natal males. Since estrogen does not readily penetrate the brain, the evidence cited for the estrogen theory involves the synthetic chemical diethylstibestrol or DES. This drug was given to pregnant females during 1940's through the 1980's but was eventually banned because it caused cancer in female offspring who were exposed through their mothers in utero.  Because of this, most of the research was conducted with exposed natal females.  Research with exposed males was initiated by DES-esposed researchers who believed that they were affected to become transgender. They started a website for DES exposed males and found that 150 of the 500 males who joined the website thought that they were transgender.  This episode provides an answer as whether the evidence supports whether DES causes being transgender and the status of the estrogen theory of being transgender.