A case story is presented of a child diagnosed by chromosome analysis to be carrier of the fragile X chromosome at a low frequency in cultured lymphocytes. DNA analysis of the FMR1 gene at a later date did not reveal expansion of the FMR1 repeat, thereby refuting the diagnosis of fragile X syndrome. The discrepancy was discovered only when years later other family members came for counselling due to subsequent development of DNA-based analyses. It is recommended that persons and families investigated before DNA methods were used are re-evaluated and re-examined when relevant. Genetic diagnoses need regular revision, and information to families is important.