Clinical trials are essential for the development of new and effective treatments for cancer; however, participation rates are low. One reason for this is lack of knowledge about clinical trials. This study assessed how often clinical trials are discussed on calls to National Cancer Institute's Cancer Information Service (CIS). The authors quantitatively analyzed 283,094 calls to the CIS (1-800-4-CANCER) over 3 years (2006-2008). They calculated descriptive statistics and multivariate regressions to determine whether specific caller characteristics are associated with the presence of a clinical trials discussion. In addition, 2 focus groups were conducted with CIS information specialists (n=12) to provide insight into the findings. The authors found that approximately 9.3% of CIS calls discussed clinical trials, with higher percentages for patients (12.5%) and family members (15.4%). Calls with Hispanics, Blacks, and Spanish speakers were less likely to include a conversation. For all cancers, patients who are in treatment or experiencing a recurrence were statistically significantly more likely to discuss clinical trials. CIS information specialists reported callers' limited knowledge of clinical trials. The CIS has the unique ability to make a substantial effect in educating patients about clinical trials as an option in cancer treatment and care.