Fragile X syndrome is the most common from of inherited mental retardation. Approximately half of females with the full mutation have significant cognitive deficits, whereas females with the premutation do not. Phenotypic effects seen in 281 females (IQs from 64 to 139) were analyzed. Results showed that females with the full mutation differ significantly from controls on selected anthropometric measurements, physical index score, and various behavioral features. Females with the premutation differed significantly from controls in regards to a few anthropometric measurements and the physical index score but not in behavioral features. These results suggest that phenotypic effects of the FMR1 mutation are not only common in females with the full mutation, but in females with the premutation as well.