Apathy, defined as a reduction in voluntary goal-directed behaviours (GDB), is one of the most common behavioural symptoms encountered in Alzheimer's disease (AD). However, the processes underlying the different components of apathy are still unclear. The aim of this study was to explore a particularly important aspect of executive function in daily life: multitasking (assessed with the Modified Six Elements Task (MSET)), and its relationship with apathy in AD. 67 participants (37 AD patients matched with 30 control participants) were screened using the MSET. Simultaneously, a close relative of each patient was given the Apathy Inventory (AI), which assesses three distinct dimensions of apathy (lack of initiative, lack of interest, emotional blunting). AD patients presented significantly more multitasking deficits than control participants. In addition, regression analyses revealed that the number of rule breaks on the MSET (inability to perform several tasks in a predefined time observing a number of rules) was the best predictor of apathy, and especially of lack of initiative. These results suggest that the relation between lack of initiative and multitasking has a specific character and that mechanisms underlying multitasking constitute a key component of GDB.