This article presents data on the large Huntington's disease (HD) family of Tasmania. Nine generations have been traced, starting with the father of the woman who brought the disease to the State. From that woman, six lines have living affected descendants. There are 765 living descendants who are "at risk" of HD. The numbers of affected males and females are equal. Affected members of the family have a mean age of onset of HD of 48.6 years and a mean age of death of 61.8 years. Affected members are at least as fertile as members of the general population. Late-onset disease is associated with significantly greater fertility (in men more so than women) compared with that of unaffected siblings of the same sex. Men with late-onset disease had a significantly older mean age of reproduction than that of their unaffected male siblings, and they had significantly more offspring than the number calculated for the general population of Tasmania. Unaffected siblings produced fewer offspring than in the general population.