The Gynecologic Cancer Study Group (GCSG) of the Japan Clinical Oncology Group (JCOG) was organized in 1994. The GCSG has developed under the leadership of three successive group representatives, five principal study investigators, the cooperation of group members and the support of several public research funds. At present, 38 institutions are participating as active members of the GCSG of the JCOG. In addition to gynecologic oncologists, medical oncologists, pathologists and radiotherapists are participating in our group. Our group manages female genital malignancies including uterine cervical, endometrial, ovarian, tubal and vulvar cancers. Because the incidences of uterine cervical (in younger women), endometrial and ovarian cancer have increased in Japan in recent years, we are developing new standard treatments especially for these malignancies. As of 31 May 2011, our group has conducted six JCOG clinical trials (three completed and three ongoing) and completed one JCOG accompanying study, which is now in preparation for publication. Our group has also conducted several retrospective studies, and Phase I and II trials independent of the JCOG Data Center. Our aim is to conduct unique and high-quality clinical trials which we can appeal to the world. In this review, we present the organization and achievements of our group, along with a list of participating institutions, as the history of the GCSG of the JCOG.