We examined desires to be involved in decisions about one's own medical treatment in a sample of 459 health maintenance organization members. Demographic variables (age, sex and education level) that have been found to be related to decision preferences were also tested. As predicted, respondents expressed a desire to be involved in decisions that do not require medical expertise, but had significantly lower preferences for involvement in decisions that required medical expertise. Younger and better-educated individuals reported a higher desire for involvement, but there were no sex differences in preferences. The higher desire for involvement in decisions not requiring medical knowledge was found both for groups that traditionally have wanted involvement and for those that have not. The implications of the results for patient participation in decision-making are discussed.