[New aspects of theories on the formation of clefts--current state of knowledge]

The theory on the origin of cleft lips and palates is briefly outlined with due regard to certain interesting aspects such as the discordance in monozygotic twins, the questions of noxae which might act at the embryonic period, the term of boundary line of the head of the foetus, the viewpoints of kinetic and dynamic embryology and the possible rôle of the premaxilla. Improvements in diagnosis by means of amniocentesis and foetoscopy provide starting points for preventive measures.