Background: The primary goals of this analysis were to explore the pros and cons of prognostic disclosure to patients and their families from the bereaved family's point of view. Methods: Semistructured interviews were conducted with 60 bereaved family members of patients with cancer in Japan. Results: There were eight categories of influence related to the disclosure of prognosis to the family, including pros (e.g., "Enabling mental preparedness for the patient's death") and cons (e.g., "Being distressed by acknowledging the patient's prognosis"); and seven categories of influence of not disclosing the prognosis to family, including pros (e.g., "Being able to maintain hope") and cons (e.g., "Being prevented from providing adequate care for the patient"). There were also nine categories of influence related to the disclosure of prognosis to patients (e.g., "Enabling various discussions regarding death with the patient"), and eight categories of influence related to not disclosing the prognosis to patients (e.g., "Maintaining the patient's hope"). Conclusions: Although prognostic disclosure to family members can contribute to psychological distress and hopelessness, at the same time, it has the potential to prepare them for the future both emotionally and practically, and also to make the time until the patient's death as meaningful as possible. It is useful for physicians to introduce pros and cons of prognostic disclosure to family members at the time of decision making, to understand the family members' psychological state, and to provide support considering pros and cons whether or not they disclosed prognosis.