This study explored patient information-seeking behavior and how such behavior might affect patient-physician interaction or health-care decisions. Telephone interviews were conducted with 257 patients with cancer and their relatives who called the National Cancer Institute's Cancer Information Service (CIS) and who received treatment-related information. Results indicated that these patients were generally very satisfied with communication from their treating physicians, had strong information needs, and preferred to participate in their treatment plans. They sought information from CIS just after diagnosis (49%) or during treatment (31%). Many of these patients (42%) discussed the CIS information with their physicians and 19% of these physicians sought more information or consulted a CIS referral. CIS referrals were contacted personally by 18% of patients. Stepwise discriminant analyses indicated that, compared with patients who did not, patients with either of these outcomes were more stressed by their disease and had been seen at more hospitals. Additionally, patients who shared CIS information with their physicians were also younger and more trusting that their physicians had current knowledge. Patients who themselves contacted a CIS referral were also more educated, had higher information needs, were less satisfied with the clarity of physicians' answers to their questions, called CIS earlier in their illness, and called specifically for a referral. Overall, these patients' most common information needs were for exploring all treatment options and being knowledgeable when discussing treatment plans with physicians. The information received from CIS satisfied these needs and was often communicated to their physicians.