Rett syndrome (RS) is characterized by progressive loss of intellectual functioning and fine and gross motor skills as well as development of stereotypic hand movement abnormalities, occurring after 6 to 18 months of normal development. Rett syndrome has been previously reported only in girls, but the possibility of the syndrome existing in male children cannot be currently excluded. Although the syndrome is thought to be relatively common, it was only described in the English literature 5 years ago. There is currently no marker for the syndrome; diagnosis is based on clinical criteria. The newly developed diagnostic criteria for RS are reviewed, with special attention given to the historical aspects of the diagnosis in the prenatal, perinatal, neonatal, and early childhood periods. Rett syndrome is characterized by a predictable, orderly progression of signs and symptoms. Four stages of RS have been described; each stage has special characteristics and offers different diagnostic challenges for the neurologist. Infantile autism is the most common incorrect diagnosis made for children with RS. The simultaneous regression of both motor and language skills, as well as the stereotypic hand movements, hyperventilation, bruxism, and seizures in early childhood are all typical in RS and help distinguish RS from infantile autism.