A questionnaire study on sexual problems occurring with multiple sclerosis (MS) was carried out with 217 patients who had previously participated in the University of Washington Multiple Sclerosis Project. More than one-half of the participating subjects were ambulatory without aids and nearly 75% did not use a wheelchair. Sexual dysfunction was reported by 56% of the women and 75% of the men. Among the women, the most commonly occurring sexual symptoms (in decreasing order of frequency) were fatigue, decreased sensation, decreased libido, decreased frequency or loss of orgasm and difficulty with arousal. Men reported the most common problem was erectile dysfunction, followed by decreased sensation, fatigue, decreased libido, and orgasmic dysfunction. Although loss of mobility, weakness and depression are not significantly associated with sexual dysfunction, spasticity and bladder dysfunction appear to be associated. However, even where these symptoms were absent, sexual dysfunction was perceived in at least 50% of the cases. The data indicate that sexual dysfunction can be anticipated in at least 50% of the women and about 75% of the men affected by MS, regardless of mobility level. It is most likely to occur in patients with spasticity and bladder dysfunction.