Identification of the genetic mutation responsible for Huntington's disease raises new ethical problems. Until 1993, the children of affected individuals had no means of knowing whether or not they had inherited the abnormal gene until they reached the age of onset of symptoms in their family. However, in families with at least two affected subjects, indirect diagnosis using markers in the 4 P 16 3 region was feasible. Direct genotypic diagnosis has been possible since 1993. The ability to predict the disease in subjects who will be healthy until the age of 40 years or so raises ethical problems. The decision to request predictive testing can be made only by the high-risk individuals themselves. Only the patient should be told of the result. Antenatal diagnosis is possible if requested by the patient or high-risk individual; in the latter case, predictive testing in the high-risk parent should be done first.