Background: Recruitment to clinical trials remains poor, and patient knowledge of clinical trials is one barrier to recruitment. To identify knowledge deficits, we conducted and compared surveys measuring actual patient knowledge and clinical trialist priorities for patient knowledge. Methods: Consenting patients at a tertiary cancer centre answered a survey that included (i) 2 opinion questions about their own knowledge and willingness to join a trial, and (ii) 22 knowledge questions. Clinical researchers at the centre were asked 13 questions about the importance of various trials factors. Results: Of 126 patients surveyed, 16% had joined a clinical trial, and 42% had a secondary school education or less. The mean correct response rate on the knowledge questions was 58%. Higher rates of correct responses were associated with lower age (p = 0.05), greater education (p = 0.006), prior trial participation (p < 0.001), agreement or strong agreement with perceived understanding of trials (p < 0.001), and willingness to join a clinical trial (p = 0.002). Trialists valued an understanding of the rationale for clinical trials and of randomization, placebo, and patient protection, but those particular topics were poorly understood by patients. Conclusions: Patient knowledge about clinical trials is poor, including knowledge of several concepts ranked important by clinical trialists. The findings suggest that when developing education interventions, emphasis should be placed on the topics most directly related to patient care, and factors such as age and education level should be considered.