Medical practice is based upon a combination of knowledge, skill, and belief. This paper traces the development of the belief system or ideology in obstetrics and gynecology from 1920 to the present. Using Presidential addresses aid other important articles from the two most prestigious obstetrics and gynecology journals, we look at what these doctors say about themselves and about women. The first period, from 1920-1944, marks the formal alliance of obstetrics and gynecology in the United States and the formation of its ideology. Part II of this article, to be published in the next issue, will begin with the expansive War and post-War years and extend to 1980 when obstetrics and gynecology finds itself under attack from all sides.