Premutation alleles of the fragile X mental retardation 1 (FMR1) gene give rise to a late‐onset movement disorder, fragile X‐associated tremor/ataxia syndrome (FXTAS), characterized by progressive intention tremor and gait ataxia, with associated dementia and global brain atrophy. The natural history of FXTAS is largely unknown. To address this issue, a family‐based, retrospective, longitudinal study was conducted with a cohort of 55 male premutation carriers. Analysis of the progression of the major motor signs of FXTAS, tremor and ataxia, shows that tremor usually occurs first, with median onset at ∼60 years of age. From the onset of the initial motor sign, median delay of onset of ataxia was 2 years; onset of falls, 6 years; dependence on a walking aid, 15 years; and death, 21 years. Preliminary data on life expectancy are variable, with a range from 5 to 25 years. © 2006 Movement Disorder Society