Presymptomatic DNA-testing for adult-onset diseases has serious psychological consequences. Here the psychological consequences of presymptomatic DNA-testing for Huntington's disease are reviewed. Both carriers and non-carriers experience emotional reactions after disclosure of their test result. However, up to today no long-term adverse emotional consequences have been revealed. Future research on other adult-onset genetic diseases should provide information about the reactions of children. In genetic counselling, attention should be paid to the reactions of people with a decreased risk. Genetic counselling must focus on the whole family and not on the individual applicant.