As progressive dementia involves changes in patients' behaviour and cognitive and functional abilities, dementia caregiving can be considered as a process that demands continuous adaptation to change. The current intervention study investigated associations between the course of dementia patients' impairment and their caregivers' well-being over two years. One hundred and twenty-eight care recipient-caregiver dyads participated in a controlled randomised intervention study (psycho-educational group intervention), 99 dyads in which the care recipients still lived at home participated in the second assessment, and 75 dyads in the third assessment. Caregivers were interviewed about their subjective well-being (emotional well-being and life satisfaction) as well as care recipients' behavioural problems and functional disability. Care recipients completed various neuropsychological tests. The assessments were repeated one and two years later. The psycho-educational intervention had a positive impact on caregivers' well-being. Level and increase in behavioural problems and increases in cognitive and functional impairment negatively affected caregiver well-being over time. For participants from the control condition the negative association between increase in impairment and decrease in caregiver well-being over time was stronger than for the caregivers in the intervention group. Our results suggest that it is not only the severity of current problems and stress, but also the rate of change, that is important for caregivers' well-being. Psycho-educational group intervention may help caregivers to adapt to the increasing impairment of care recipients with dementia.