This study applied the theory of planned behaviour (TPB) to the prediction of breast self-examination (BSE) intentions and behaviour, and tested whether the frequency of past behaviour and context stability moderates intention-behaviour and habit-behaviour relations. Seventy-seven females completed measures of the TPB, frequency of past behaviour, context stability and habit strength (Self-Report Habit Index). BSE behaviour was assessed at 1-month follow-up (n = 66). The TPB explained 33% of the variance in BSE intentions and 11% of the variance in time 2 BSE. The frequency of past behaviour moderated the intention-behaviour relationship such that the intention was only positively related to time 2 BSE behaviour when the frequency of past behaviour was low. Context stability and the combination of the frequency of past behaviour × context stability moderated the habit-behaviour relationship such that habit strength was only positively related to time 2 BSE behaviour when context stability and the combination of frequency of past behaviour × context stability were high. The results are consistent with the proposal that behaviours that are performed frequently in stable contexts are predominantly under the control of habitual processes, whereas behaviours that are performed infrequently in unstable contexts are predominantly under the control of intentional processes.