Dementia has become a public health priority along with population ageing worldwide. Owing to its chronic progressive nature in the absence of a cure, maintaining the best possible quality of life (QOL) has become the desired outcome for people with dementia. The aim of this study was to compare the Quality of Life (QOL) of patients with dementia in Sri Lanka when assessed based on the patient’s and caregiver’s perspectives. A cross-sectional study was conducted among 272 pairs of patients with dementia and their primary caregivers recruited systematically from the psychiatry outpatient clinics of tertiary care state hospitals in the district of Colombo, Sri Lanka. The QOL was assessed using the 28-item DEMQOL among patients and the 31-item DEMQOL-proxy among primary caregivers. The total QOL ratings and subscale scores obtained by patients and caregivers were compared and assessed for the significance of the mean scores using the independent t-test and of the mean difference in ratings using the Wilcoxon test. Agreement between patients and their caregivers on the ratings for QOL was also assessed using the Bland Altman plot. The mean overall QOL score according to patient ratings (mean = 79.7; SD = 12.0) was significantly higher than the caregiver ratings (mean = 70.6; SD = 12.3) (p< 0.001). Mean scores for the four subscales (positive emotion, negative emotion, memory, and daily life) were also significantly higher according to the patient’s ratings (p<0.001). Total scores obtained by patients and their caregivers showed a positive and significant correlation (r = 0.385; p<0.001). Bland Altman plot demonstrated acceptable agreement between their ratings. The study confirms the ability of dementia patients with mild to moderate severity to successfully rate their own QOL. Furthermore, the caregiver’s ratings cannot be substituted for the patient’s ratings and vice versa.