Since the end of the twentieth century the number of birth by caesarean section (CS) has increased. In Poland in 2014, 42,8 % of deliveries was CS. On the one hand the number of maternal and newborn deaths decreases, but on the other hand caesarean section should be performed only if it is medically necessary. Alarming are reports that cesarean delivery may increase the risk of : autoimmune diseases, childhood allergies and asthma. The scientists from Italy carried out a study which showed that the intestinal flora of caesarean and vaginally delivered infants appears to be very different.