The primary aim of this study was to compare quality of life (QoL) in patients with Dementia with Lewy Bodies (DLB) and patients with Alzheimer disease (AD). The secondary aim of this study was to investigate determinants of QoL in DLB. Thirty-four patients with DLB at the Neuropsychiatry clinic, University Hospital MAS, Malmö, Sweden, were included in a cross-sectional study. These patients were matched to 34 patients with AD. Two QoL instruments, the EQ-5D instrument and the Quality of Life-Alzheimer disease (QoL-AD) instrument, were applied in this study. Both instruments were administered to both patients and caregivers. Patients with DLB in this study have significantly lower QoL than patients with AD regardless of instrument or whether patient or caregiver-reported QoL was used. Furthermore, this study shows that important determinants of QoL in DLB include Neuropsychiatric Inventory score, independency in instrumental activities of daily living, whether the patient is living with the caregiver and the presence of apathy and delusions.