Background: Immunotherapy is a novel treatment paradigm that has improved survival for patients with advanced melanoma and lung cancer and poses new risks of immune-related adverse events, which are important for patients to recognize promptly. We aimed to describe patients’ knowledge about the risks and benefits of immunotherapy, and their understanding of the goal of treatment with immunotherapy. Methods: We conducted a cross-sectional study of patients at a single institution who had initiated therapy with an immune checkpoint inhibitor for advanced melanoma, small cell lung cancer, or non-small cell lung cancer in the past 12 weeks. We assessed patients’ knowledge about immunotherapy with a 9-item knowledge questionnaire (score range 0-100; higher score represents greater knowledge). We used the Perception of Treatment and Prognosis Questionnaire to assess patients’ understanding of the goal of their treatment. We used the two-sample t-test to compare knowledge scores and chi-square test to compare goals of therapy between patients with melanoma and lung cancer. Results: A total of 105 patients (57 with melanoma, 48 with lung cancer) completed the study questionnaire. Participants had a median age of 69 years (range 36-89), and 33% (35/105) were female. Participants’ mean knowledge score was 69.0 (SD = 23.3). Overall, 91% (96/105) of patients endorsed that immunotherapy works by turning on the body’s immune system to recognize and attack cancer cells and 33% (35/105) correctly identified that immunotherapy does not kill all rapidly dividing cells. With respect to immunotherapy side effects, 68% (71/105) of patients reported that immunotherapy side effects can affect any organ in the body and 65% (68/105) endorsed that side effects from immunotherapy can occur at any time, even after the treatment ends. Overall, 34% (36/105) of participants reported that the primary goal of their treatment is to cure their cancer. Participants with melanoma had higher mean knowledge scores compared to those with lung cancer (74.7 vs. 62.3, P = 0.003). Participants with melanoma were also more likely to report that the goal of their immunotherapy was to cure compared to those with lung cancer (58% [33/57] vs. 6% [3/48], P < 0.001) and that their oncologist had said that immunotherapy would cure their cancer (19% [11/57] vs. 0% [0/48], p = 0.005). Conclusions: We observed substantial knowledge deficits about immunotherapy and perceptions that immunotherapy is a cure for advanced cancer, particularly among patients with melanoma. These findings underscore the need for interventions to enhance patients’ knowledge about immunotherapy and to help them understand the goal of immunotherapy for patients with advanced cancer.