Rett's syndrome is a neurodevelopmental disorder which is caused by a mutation on the x-chromosome; thus, it only affects the female sex. After seemingly normal postnatal development affected girls lose already acquired mental, motoric and social skills. The last stage of the syndrome is characterized by microcephaly, severe mental retardation, spastic paraparesis, epilepsia, respiratory dysrhythmia, neurogenic scoliosis, abnormal joint alignment and muscle contractures. Rett's syndrome is probably the leading cause for progressive mental retardation in girls, but still it is relatively unknown. This paper describes Rett syndrome and its pathophysiology. The following case report discusses special anesthesiological implications due to the immature cardiorespiratory system and describes a coagulation disorder following treatment with valproic acid.