On the basis of our own experience and the literature the risk of acidosis, which corresponds to the risk of asphyxia, during vaginal delivery of breech presentations is examined. Compared with delivery of vertex presentation it is 3-10 times greater. The risk of acidosis does not depend on the duration of pregnancy and only a little on the parity of the mother. Even with carefully selective indication for primary Caesarean section it cannot be reduced below the high level. Typically there is acute compression of the cord at the end of the first or later stages of labor. Even with intensive intra-partum care it cannot safely be predicted with sufficient certainty. As a criterion of the efficiency of modern obstetrics the impact of acidosis in umbilical blood and its increase in breech presentation is discussed. Only systematic Caesaren section before or early in labor will lower the risk to that of vertex presentation. This is done and recommended by the authors. Links between acdosis in umbilical blood and permanent cerebral damage are probable but by no means certain and their importance in unknown. Selective indication for Caesarean section which has to be made generously, represents an acceptable alternative.