Purpose: To know how traditional midwives build their maternal health knowledge and how they relate with health institutions. Methods: A qualitative study was carried out in 2005. In such study eight traditional midwives were interviewed at their homes, and three antenatal consultations and two training courses for midwives were assessed in Morelos, Mexico. Interview and observation guidelines included topics such as the beginnings as a midwife, the relation with health institutions as well as the observance of traditional and biomedical practices. Results: Traditional midwives combine traditional and biomedical knowledge. The latter is a result of the influence of health institutions carried out through training courses. These women have been exposed to the rejection attitude of physicians that has generated relationship conflicts, the situation leading them to hide their midwife nature or not to escort their patients to medical consultation in order to preserve their patient's physician medical care. As a means of resistance before the medical criticism, they carry out traditional practices they consider beneficial to women. Conclusions: The medicalization process prevailing in health institutions has had a significant impact on traditional midwifery. Midwives have been exposed to exclusion and illegitimation of their traditional practices, however, they have acquired biomedical knowledge to improve the quality of the care provided.