In Japan, family caregivers of newly diagnosed patients with cancer usually receive information on the patient from healthcare professionals before patients are told the truth. Efforts to provide suitable information to these caregivers may be crucial to improving the quality of life in patients as well as in family caregivers. A descriptive correlational study explored and assessed the informational needs of family caregivers of newly diagnosed patients with cancer. Data were obtained by a semistructured interview with a questionnaire administered to 66 caregivers. Information needs were assessed on disease, treatment, prognosis, and patient and family care. In addition, the demographic and situational characteristics related to individual information needs were investigated by logistic regression analyses. More than 70% of caregivers wanted the disease-related information and about one third of those wanted the care-related information for the patient and family. The disease-related information needs had significant correlations only with the demographic variables. The care-related information needs were correlated both with the demographic variables and with the situational variables such as the presence of pain in the patient and the presence of other family caregivers. Our results may help healthcare professionals to plan the appropriate provision of information to newly diagnosed patients with cancer and their family caregivers.