PURPOSE: Patients with advanced cancer often have unrealistic expectations about prognosis and treatment. This study assessed the effect of an oncology nurse-led primary palliative care intervention on illness expectations among patients with advanced cancer. METHODS: This study is a secondary analysis of a cluster-randomized trial of primary palliative care conducted at 17 oncology clinics. Adult patients with advanced solid tumors for whom the oncologist would not be surprised if died within 1 year were enrolled. Monthly visits were designed to foster realistic illness expectations by eliciting patient concerns and goals for their medical care and empowering patients and families to engage in discussions with oncologists about treatment options and preferences. Baseline and 3-month questionnaires included questions about life expectancy, treatment intent, and terminal illness acknowledgment. Odds of realistic illness expectations at 3 months were adjusted for baseline responses, patient demographic and clinical characteristics, and intervention dose. RESULTS: Among 457 primarily White patients, there was little difference in realistic illness expectations at 3 months between intervention and standard care groups: 12.8% v 11.4% for life expectancy (adjusted odds ratio [aOR] = 1.15; 95% CI, 0.59 to 2.22; P = .684); 24.6% v 33.3% for treatment intent (aOR = 0.76; 95% CI, 0.44 to 1.27; P = .290); 53.6% v 44.7% for terminal illness acknowledgment (aOR = 1.28; 95% CI, 0.81 to 2.00; P = .288). Results did not differ when accounting for variation in clinic sites or intervention dose. CONCLUSION: Illness expectations are difficult to change among patients with advanced cancer. Additional work is needed to identify approaches within oncology practices that foster realistic illness expectations to improve patient decision making.