Her research has included a wide range of studies on determinants of sexual risk behavior among children, adolescents, heterosexual women and men, and the gay population, and on comprehensive approaches to preventing HIV and STD infection.
A native of Hamburg, Germany, Ehrhardt completed a doctorate in clinical psychology at the University of Düsseldorf in Germany based on her pioneering work at Johns Hopkins University in the field of human gender and sexual development under the mentorship of sexologist John Money.
With Money, she co-authored Man & Woman, Boy & Girl: Gender Identity from Conception to Maturity, a landmark 1972 book in the field of sexuality studies.
Ehrhardt arrived at Columbia University in 1977, and in 1987 founded the HIV Center with what was then the largest single grant ever awarded by the National Institute of Mental Health.
She has also been a member of the National Institutes of Health (NIH), Office of AIDS Research Advisory Council, the executive committee of the HIV Prevention Trials Network of Family Health International, and the Board of Trustees of the Kinsey Institute for Research in Sex, Gender, and Reproduction.