Causes of death were examined from death certificates for 395 Danish subjects with Huntington's disease (HD) and for 282 unaffected sibs and compared with the causes of death in the general Danish population. For both the HD subjects and the sibs, pneumonia and cardiovascular diseases were the most frequent primary causes of death. Suicides accounted for 5.6% of all deaths among the HD subjects and, unexpectedly, for 5.3% among the sibs, some of whom may have been carriers of the HD gene. Both were significantly higher than the corresponding frequency of 2.7% in the general Danish population, but there was no evidence of differences in the age specific proportions for the HD subjects and for the sibs compared to the general population. Some accidents leading to death in the sibs may have been hidden suicides. The rate of cancer was low for the HD patients, being only 5.3% compared with 31.2% for the sibs. Neurological diseases were reported with an increased frequency in the HD patients compared to the general population, 6% v 1%.