Huntington's disease (HD) and multiple sclerosis (MS) are both chronic progressive illnesses posing a serious challenge to affected patients and families. Sexual dysfunction in HD as well as in MS is a very common problem, although it is unclear whether the dysfunction is caused by the chronic illness itself or by the sociopsychiatric burden related to the illness. Twenty-nine patients with HD and 27 patients with MS each participated in a semistructured interview and several standardized questionnaires concerning partnership, sexual function, and body image. The results display significant differences in both patient groups, displaying higher sexual desire and activity in HD patients, but MS patients also reported fewer sexual problems compared to the norming values. Conversely, the MS patients' relationships seemed to be stable despite subjectively perceived lower initiative on sexual activities. The results are discussed under the possible influences of the underlying organic changes and the psychosocial consequences of chronic progressive disorders.