Anxiety is a common symptom in patients with advanced cancer. Early recognition of anxiety is difficult, especially when the physical condition of patients declines and patients are not able to verbally express about their concerns. Under these circumstances, informal caregivers may be a valuable source of information. The aim of this study was to explore anxiety in hospice inpatients with advanced cancer from the perspective of their informal caregivers. Fourteen informal caregivers were interviewed; 64% were women and the median age was 55 years. Informal caregivers assessed patients' anxiety as moderate to severe and identified a negative impact of anxiety on physical, psychological, social, and spiritual dimensions of the patients' lives. They indicated a variety of expressions of anxiety and mentioned physical and mental deterioration as an important source of anxiety. Informal caregivers recognized patients' needs as having a safe environment, presence of people around, and a sense of control over the situation. Although the patients' perspective is the gold standard, informal caregivers can be a valuable source of information in identifying anxiety and providing personalized support. Therefore, informal caregivers should be more involved in the care for anxious patients to improve early recognition of anxiety and to ameliorate anxiety management for this vulnerable patient population.