Four offspring of three different Huntington disease (HD) affected x affected matings were assessed by genetic linkage analysis for possible homozygosity. One individual was found to have a 95% likelihood of being an HD homozygote. The homozygote individual had an age at onset and symptoms which were similar to those of affected HD heterozygote relatives, including some with younger onset. This confirms the observation of Wexler et al. that in HD the homozygote is not more severely afflicted than the heterozygote.