Fragile X syndrome is the most common cause of mental retardation in the male. Historically, fragile X premutation was considered to be phenotypically silent. In recent reports the premutation has been associated with premature ovarian failure and fragile X-associated tremor/ataxia syndrome. This case describes a 24-year-old woman who presented with irregular menstrual cycles secondary to premature ovarian failure. Subsequent genetic analysis confirmed that she has a premutation for fragile X with 70 CGG trinucleotide repeats.