SummaryBirdet al. (1974) noted an interesting ‘anticipation’ phenomenon in Huntington's Chorea occurring in patients who inherited the gene from their father. More extensive samples from 165 pedigrees in the Low Countries permitted us to show that most of this apparent ‘anticipation’ is an artifact due to sampling biases related to the year of birth categories of the affected parents. When these biases were excluded no differences exist between the ages of death of affected mothers and their affected children, but a small difference of approximately two ymrs remains between affected fathers and their affected children. This is explainable by the observation that juvenile cases of Huntington's Chorea usually have inherited the abnormality from their