Unlike in other chronic diseases, the Quality of Life (QoL) of patients affected by Alzheimer Disease (AD) has not been well established, primarily because of the difficulties stemming from the study of patients with cognitive disorders. Because no cure is currently available for AD, the optimization of QoL represents the best possible outcome attainable in all stages of disease, making QoL assessment mandatory. This study identified variables related to patients' QoL and examined the agreement between patients' and caregivers' QoL ratings. A total of 135 dyads (patient and principal caregiver) were enrolled in the study. Patients' QoL evaluations showed a negative relationship with depressive mood and a positive relationship with Activities of Daily Living (ADL), whereas caregivers' QoL ratings showed a negative relationship with patients' depressive mood and behavioral disturbances. Caregivers tended to underestimate patients' QoL compared with the patients' own self-evaluations, with patients' dependency in performing ADL and behavioral disorders as well as caregivers' burdens and depression being the main factors associated with the discrepancy in these evaluations. These findings suggest that the use of proxies as a substitute for the self-report of QoL data should be treated with caution, always accounting for the presence of potential bias.