Regular mammography facilitates early detection of breast cancer, and thus increases the chances of survival from this disease. Daughter-initiated (i.e. upward) communication about mammography within mother– daughter dyads may promote mammography to women of screening age. The current study examined this communication behaviour within the context of the Theory of Planned Behaviour (TPB), and aimed to bridge the intention-behaviour gap by trialling an implementation intention (II) intervention that aimed to facilitate upward family communication about mammography. Young women aged 18–39 (N¼116) were assigned to either a control or experimental condition, and the latter group formed IIs about initiating a conversation with an older female family member about mammography. Overall, those who formed IIs were more likely to engage in the target communication behaviour, however the intervention was most effective for those who reported low levels of intention at baseline. Perceived behavioural control emerged as the most important variable in predicting the target behaviour. The altruistic nature of this behaviour, and the fact that it is not wholly under volitional control, may have contributed to this finding. Future studies that systematically explore the relative roles of intention and perceived behavioural control in behaviours of this nature are warranted.