The present study focuses on the dyadic relationship between a family carer and a patient. Besides clarifying the quality of the caregiving relationship in two populations of chronically ill patients, this investigation examines whether patient characteristics, carer characteristics and network characteristics are predictive of relationship quality in dementia caregiving. Partners, children or children-in-law caring for a relative suffering from dementia (N = 144) and partners or parents of persons suffering from chronic mental illness (N = 77) were interviewed with a semi-structured questionnaire. The measurement of relationship quality is based on the literature of Expressed Emotion and covers two dimensions: the level of criticism and the level of warmth. In general, the relationship between a carer and his or her chronically ill relative was marked by a low level of conflict or criticism and a high degree of warmth. The main predictors of a poorer relationship quality were disturbances in the patient's behaviour and the carer's perception of these disturbances. Our results suggest that, rather than limiting investigations to the burden experienced by the family carer, future research and interventions on chronically ill patients should focus on the quality of the carer-patient relationship and its determinants.