Klinefelter's syndrome complicated with West syndrome in a 4-month-old boy.

We, for the first time, report a boy with West syndrome associated with Klinefelter's syndrome. He developed episodes of repetitive tonic spasms at the age of 4 months. He had developmental delays and hypsarrhythmia on interictal electroencephalography recording. His karyotype turned out to be 47, XXY, while we failed to observe anomalies in his appearance. Adrenocorticotropic hormone therapy with antiepileptic drugs resulted in cessation of tonic spasms, and his developmental quotient was improved by the age of 1 year. Further studies are needed to determine the causal association between West syndrome and Klinefelter's syndrome.