CONTEXT: While prognostic awareness has been commonly assessed as perceived illness terminality in patients with advanced cancer, both perceptions of illness severity and terminality may be correlated with symptom burden and quality of life. OBJECTIVES: The present study examined physical and psychological symptoms, quality of life, and smoking status in relation to perceived illness severity and terminality in patients with advanced, inoperable lung and prostate cancer. METHODS: Patients (N=198) were recruited from hospitals in the midwestern U.S. to complete a one-time survey. Prognostic awareness was assessed in the following categories: "relatively healthy," "seriously ill but not terminally ill," or "seriously and terminally ill." RESULTS: Only 12% reported an accurate prognostic awareness ("seriously and terminally ill") and 66% perceived themselves as "relatively healthy." Higher levels of anxiety, depressive symptoms, fatigue, and pain and worse quality of life were associated with a higher likelihood of reporting serious illness, irrespective of perceived illness terminality. Smoking status was unrelated to prognostic awareness. For patients with advanced lung cancer, greater breathlessness was associated with a higher likelihood of reporting serious or terminal illness. CONCLUSION: Our findings suggest that perceiving cancer as serious, not just terminal, is related to symptom burden and quality of life. Results point to the need for interventions to improve prognostic understanding and coping with the disease.