Reff syndrome is neurodegenerative disorder in girls characterized by globol deceleration of psychomotor development and subsequent loss of acquired cognitive and motor skills, occurring after 6~18 months of apparently normal development.

In 1966, Andreas Rett reported 31 girls who had mental regression, abnormal neurologic examinations, curious and repetitive hand-wringing, stereotypic movements, and other peculior behavioral manifestations.

There is no known biologic market for Rett syndrome. So diagnosis should be focused on well-defined clusters of developmental and clinical deviations.

We experienced one case of Rett syndrome in 4 years old girl and reported the case with clinical, rediologic, histologic findings.