Mental retardation (MR) consists of a sub average general intellectual functioning (IQ < 70) that is associated with significant limitations in adaptative functioning which begins before age 18 years (DSM IV). It's our intention to characterize the children's population with MR observed at the Dona Estefânia Hospital Development Center, trough a retrospective study of the children which were assessed between January 2005 and June 2007. Epidemiologic data, like the severity of DM, organic aetiologies, co-morbidity and therapeutical and educational intervention, were the parameters evaluated. There were 232 children assessed and 185 had MR, mainly boys (58%): 112 (46%) had mild MR, 54 (29%) had moderate MR, 17 (9%) had severe DM and 2 (1%) profound MR. Aetiologies were defined on 86 children (46%); the highest rate of diagnosis occurred on the most severe cases of MR. The aetiologies most frequently found were the genetic diseases, prematurity and associated comorbidity, with high variety of aetiologies. Co-morbidity was detected on 123 children (66%), being the most frequent the ophthalmologic (57 children, 46%). The totality of children with MR were proposed for early intervention (47%) and special education (58%). The data obtained from the clinical and functional characterization of the children accompanied by the Development Center of Dona Estefânia Hospital with MR diagnosis was similar to the data described in literature. However, some data differ from other case series due, among other things, to etiological group differences, different age groups and different assistential politics.