This study examined responses of 21 lung cancer outpatients to questions about their desired and actual levels of involvement in treatment decisions, and about information needed for treatment decision-making. A 'treatment trade-off' interview was used to assess patients' preferences for hypothetical treatment options. Desired roles in decisions are examined in relation to treatment preference and information needs. Forty-three percent of patients recalled desiring an active/collaborative role in their real treatment decision. For 29% of patients, there was a discrepancy between their recalled desired role and their recalled actual role; in each of these cases the patient had been less involved in the decision than they had desired. At the time of the interview (mean 26 months post-treatment), 57% of patients desired an active or collaborative role in treatment decisions. The majority of patients rated the following types of information as 'essential' to treatment decisions: details of the treatment regimen, early and late side-effects, survival, and effects of treatment on disease symptoms. The data suggest that: we should be attentive to the individual's desired role in treatment decisions at each step of care to avoid a mismatch between desired and actual involvement; desired role in decision-making does not predict treatment preference; and patients generally want a wide variety of information on treatment options in order to participate in treatment decisions.