The occipito-posterior position has been thought to be a presentation leading to dystocia as a result of faulty positioning of the head. Closer observation of the facts lead one to think that this kind of position is really the result of better accommodation of the fetal head to the shapes of pelvis to which one has not become used but which are normal: this means those where the antero-posterior diameters are greater. By itself the occipito-posterior position cannot give rise to true complications. It only needs a particular mechanism. In deliveries in the occipito-posterior position progress and prognosis depend less on the presentation than on the conditions, especially the anatomical conditions, which have given rise to or made more likely the position and which go with it. It is therefore these conditions that have to be recognized each time and taken note of in order to carry out the best possible treatment.