Rett syndrome was first described in 1966 by Dr Andreas Rett, who reported in German his findings in 22 patients. Recognition of the syndrome grew slowly until 1983, when a series of 35 patients from several countries was reported in English. By 1987, the number of known cases had grown to over 1,250 worldwide, the International Rett Syndrome Association had been founded, and international conferences on the syndrome were being held regularly. Although a developmental staging system has been devised, many questions remain concerning the course of the disease. Rett syndrome poses a challenge to the physicians, therapists, psychologists, educators, and families involved with affected patients, as well as to researchers investigating the syndrome.