A characteristic pattern of stereotypic and self-injurious behavior (SIB) distinguishes Smith-Magenis syndrome from many other genetic disorders. We examined the prevalence and severity of 11 specific types of SIB in 29 children and adults with Smith-Magenis syndrome. We confirmed the near universal presence of SIB in people with this disorder. The overall prevalence of SIB was found to increase with age as was the number of different types of SIB demonstrated by individuals with Smith-Magenis syndrome. The number of different types of SIB exhibited was also directly correlated with level of intellectual functioning. Our data suggest that with increasing age and ability levels, people with Smith-Magenis syndrome add to their repertoire of SIB from among a small number of specific behaviors.