In the UK, there are around 1.5 million carers of people with mental health problems providing substantial amounts of free care. Despite having a legal right to a ‘carer's assessment’, only a minority of mental health carers have had such an assessment. To try and understand why the uptake is so low, we undertook a small (n = 8) qualitative study exploring what mental health staff acting as ‘care co‐ordinators’ thought the barriers to, and facilitators of, carers' assessments might be, and how subsequent practice might be improved.We found that there was some confusion over the definition of ‘carer’ and over who should take responsibility for carer assessments. The main barriers to carers' assessments were the documentation used, the attitudes of staff (especially managers) and the fact that the needs of mental health carers often differed from those caring for people with a physical disability. Practice could be improved through: clarifying the definition of ‘carer’; education and training; redesigning the documentation; dovetailing service user and carer needs assessments; and through offering a wider choice of evidence‐based services as assessment outcomes. Improvements are unlikely to be successful, however, without the active support, expertise and engagement of carers.