Background: This study aims to identify met and unmet needs, according to the patient, the carer and the staff, and their relationship with socio-demographic and clinical characteristics in elderly people with mental health problems. Methods: A sample of 306 elderly patients 65 years, of both sexes, diagnosed with mental illness (ICD-10 criteria), was recruited from inpatient/outpatient settings in a Department of Psychiatry and Mental Health, in northern Portugal. Patients were assessed with the Camberwell Assessment of Need for the Elderly/CANE. Results: The majority of diagnoses were depression (33.7%), dementia (24.5%), and schizophrenia (12.7%). The patients' main unmet needs found were psychological distress (15.0%), daytime activities (10.5%), and benefits (6.5%). Patients reported significantly lower unmet and global needs than carers and staff (Z = -8.58, p < 0.001; Z = -11.07, p < 0.001, respectively). A larger number of global needs (met and unmet) were associated with the diagnosis of dementia, followed by schizophrenia, bipolar, and depressive disorder (p < 0.001), with inpatients reporting more needs than outpatients. Conclusions: Mental disorders were associated with a greater number of needs in elderly patients, which makes this assessment important as it includes the patients' perspective, when they are the focus of intervention, in order to decrease distress and make more beneficial use of services, especially in inpatient settings. These different perspectives are crucial when assessing and planning psychiatric and mental health services.