Objectives Caregivers of terminal patients often report a higher prevalence of unmet needs than cancer survivors. However, very few interventions have been carried out to support caregivers of patients in advanced stages, and, in most cases, they have not been rigorously designed and evaluated. The ultimate aim of this research was to obtain specific information about the sociodemographic characteristics, the different types of care provided, the symptoms due to burdens, the impact of caring on the quality of life, and the unmet needs of informal caregivers of dependent patients with cancer. This is to design effective intervention programs that can be implemented from the hospital setting itself and therefore, to improve their quality of life and prevent the deterioration of their health. Study design A cross-sectional design and survey methodology were used for descriptive purposes. Methods The sample was composed of 132 informal caregivers of dependent patients with cancer, from a public hospital in Valencia, Spain, who were identified through the patient database of the oncology service, over the 4-month data collection period. Self-administered questionnaires were combined with personal interviews: Interview Protocol for the main caregiver, Questionnaire ICUB97, and survey of hospital quality. Results The most frequently provided types of care included the following: keeping the patient company, acting as an intermediary between them and healthcare workers, and helping them to do basic daily life activities. The main negative consequences caregivers reported were the following: feeling more tired, having less free time, changing their daily routines, and having fewer social relationships/interactions and various emotional and physical symptoms. Many of the needs of informal caregivers were not being met: resolution of doubts about illness, training in the care they should provide to the patient, and psychological help. Conclusions Recommendations for the development of effective intervention programs are offered: increasing the psychological services provided in oncology units, training medical staff in communication skills, facilitating access to information about the disease through different means, training for informal caregivers in care techniques, coping and communication skills, self-care, and organization of time. On the one hand, implementing effective intervention programs for informal caregivers will reduce the amount withdrawing from their care duties and on the other hand, the proliferation of what are known as secondary patients. Highlights • Caregiving women were more prevalent than men, with an average age of 45 years, and a medium socioeconomic status. • The most frequently provided cares were helping patients in basic activities and mediating between them and medical staff. • The main negative consequences for caregivers were changing daily routines and various emotional and physical symptoms. • The main unmet need of caregivers was specific information and training about the care they should provide to the patient.