Objectives: We investigated the factors associated with discrepancies between patients' and caregivers' ratings about patients' general QoL and about the domains of Quality of Life in Alzheimer's disease Scale (QoL-AD) at baseline and 12 months. Methods: Longitudinal study composed by 114 outpatients with Alzheimer's disease and their caregivers. Patients were assessed with the QoL-AD, Mini Mental State Examination, Assessment Scale of Psychosocial Impact of the Diagnosis of Dementia, Cornell Scale for Depression, Functional Activities Questionnaire, Neuropsychiatric Inventory and Clinical Dementia Rating Scale. Caregivers answered the QoL-AD, Zarit Burden Interview and Sociodemographic Questionnaire. Results: Linear regression analyses indicated that the factors associated with discrepancies of patients' and caregivers' ratings of patients' QoL-AD were impaired awareness and caregiver burden at baseline and impaired awareness at 12 months. Also, the factor associated with discrepancies in domain memory was impaired awareness and in domain ability to do chores, impaired awareness and functional deficit. Conclusions: The discrepancies between patients and caregivers were related to awareness and caregiver burden at baseline and to awareness at 12 months. These results raise questions regarding the subjective nature of QoL and the validity of patients' evaluation about their own QoL.