The accuracy of the knowledge of genetic patterns of Huntington's disease was studied by interview in 14 patients who had been in regular contact with physicians. Only one patient had completely accurate knowledge of the genetic risk entailed by autosomal dominance. Inaccurate knowledge often prevented optimal judgment concerning major life decisions. The genetic risk problem almost invariably generated severe psychologic problems, particularly centered about the decision whether to have children. Genetic counseling, particularly in a progressive disease of adult onset such as Huntington's disease, must be accompanied by follow-up visits to ascertain the accuracy of the knowledge obtained and to aid the patient in resulting psychologic problems.