Using the Huntington's disease register for South Wales, a total of 86 affected individuals were identified living in the counties of Mid Glamorgan, South Glamorgan and Gwent, giving a point prevalence rate for Huntington's Disease in South East Wales of 6.2/100,000. Only four (4.7%) of these individuals developed their symptoms after the age of 60 years. A subsequent retrospective search of the register identified a total of 33 individuals with clinical evidence of Huntington's disease and whose age of onset of symptoms occurred between the ages of 60 and 77 years. In this group the median time for disease duration from the onset of symptoms was 13 years (range 0.5-25 years), with survival up to age 86 years recorded. Initial symptoms of Huntington's disease included disturbance of gait in 32 individuals; 31 had involuntary movements, and 20 had abnormality of speech. Major psychiatric symptoms were present in only six cases; but approximately a third (ten cases) had symptoms related to impaired cognitive function. Molecular analysis was possible on ten individuals in the series. The expanded CAG repeat sequence in the Huntington's disease gene was found in all cases, with a narrow range of 36-38 repeats, representing the smallest repeats seen in our Huntington's disease group. Our study suggests that Huntington's disease in elderly people causes predominantly motor disturbance at onset with relatively mild disability and a favourable outlook for both independent living and for life expectancy. However, the potential for under-diagnosis in this age group may have considerable genetic consequences, with transmission of the disorder to numerous descendants by the time its hereditary nature is recognized.