A study was performed on a family from Cali, Colombia in which nine patients were evaluated, three of which presented with intellectual disability with no previous etiological diagnosis. The proband was diagnosed with Fragile X syndrome by DNA molecular testing and, cascade testing, performed on all available family members, identifying two additional individuals with the full mutation and four carriers of a premutation allele. With this report we seek to contribute to Colombian epidemiology of the syndrome and emphasize the importance of diagnosis to provide a comprehensive and specific treatment to those affected. Further we seek to identify premutation carriers in their families or women with a full mutation without the classic phenotype for genetic counseling and education about potential associated pathologies.