The rate of occurrence of conduct disorder and affective illness was studied for a sample of 112 offspring of 34 Huntington's Disease (HD) patients. Psychiatric disorder in the offspring was assessed as a function of: (1) age of the parent at the onset of symptoms of HD; (2) family disorganization; and (3) psychiatric disorder in either parent. The findings indicated an increased frequency of conduct disorder in disrupted families, most especially in those where the HD parent had an early onset of symptoms and the non-HD parent showed psychiatric disorder. Affective disorder in the offspring was most strongly associated with the presence of similar symptoms in the HD parent. Affective disorder, but not conduct disorder, may be an early manifestation of the HD gene. The implication of these findings for genetic counselling is discussed.