Sex chromosome abnormalities are among the most frequent aneuploidies, occurring in 1:400 newborns. The 47, XYY syndrome, with an incidence of about 1:1000, is difficult to recognize clinically because of the presence of non specific dysmorphic signs, especially in younger children. We describe a case of 47, XYY syndrome, who had tall stature, macrocephaly, mental retardation, minor dys­morphic features and behavioral problems. These children need to be closely monitored in order to evaluate all problems that appear throughout their life. Psychological counseling is needed for control of their impulsiveness. Detailed information should be obtained about their fertility rate and the risk for their future offspring. Such information is essential for parental decision following prenatal diagnosis.
Key words: XYY Syndrome, Tall stature, Minor dys­morphic signs.