The experience and construction of caring in 50 informal cancer carers, 35 women and 15 men, was examined using a critical realist approach and a mixed method design. Women reported higher rates of depression, anxiety, unmet needs and burden of care than men. No gender differences were found in time spent care-giving, suggesting that gendered roles are implicated in distress and coping. Semi-structured interviews with 13 carers were used to identify gender differences in caring, analysed using positioning theory. Women described being positioned as all encompassing expert carers, expected to be competent at decision-making, a range of physical caring tasks, and provision of emotional support for the person with cancer. The consequences of this positioning were over-responsibility and self-sacrifice, physical costs and overwhelming emotions, which were self-silenced. In contrast, men carers positioned caring as a competency task which they had mastered, and which provided them with satisfaction, with the emotions of the person with cancer, or their own emotions, being negative aspects of caring. It is concluded that cancer caring is tied to gendered constructions and expectations, with considerable implications for psychological well-being and coping, and for carer support services, which need to take gender issues on board.