In recent years, a number of articles have appeared in the literature concerning the fragile X syndrome; however, in few cases was the diagnosis of the syndrome in young children discussed. A review of 20 children younger than 7 1/2 years of age who had the fragile X syndrome seen at the Cincinnati Center of Developmental Disorders was undertaken in an attempt to establish guidelines that would aid the practicing physician in determining which children should have a chromosomal analysis. All children were developmentally delayed; 95% had speech delays. Short attention span with hyperactivity, temper tantrums, mouthing of objects persisting at an age beyond when it would be expected, autistic behaviors, and poor gross motor coordination were seen in 50% or more of the children. Mental retardation was present in the family history of 65%, and 90% had a family history of at least one of the following: mental retardation, learning disabilities, or hyperactivity. The most common physical findings were long and/or wide and/or protruding ears, prominent jaw and/or long face, high arched palate, and a flattened nasal bridge. The fragile X syndrome can be recognized by noting key aspects of the behavioral and family histories as well as the physical findings.