Objectives: To assess the sensitivity of patients who suffered a severe closed-head injury to the manipulation of attentional resources and encoding instructions during the execution of prospective memory tasks.Material and Methods: A group of patients with chronic sequelae of severe closed-head injury and a group of matched normal controls were given an experimental procedure for the assessment of time-based and event-based prospective memory. Availability of attentional resources at the time of intention recall and encoding conditions at the time of giving instructions were varied across experimental sessions.Results: The simultaneous execution of a concurrent task was more detrimental to accuracy in the spontaneous recall of the prospective intention in the post-traumatic than in the normal control group. Moreover, the instruction to encode more extensively by rehearsing aloud and mentally imaging the actions to be performed at the time of the study improved recall accuracy more in the post-traumatic than in the normal control group.Conclusions: Based on these data, we suggest that a prospective memory deficit in post-traumatic patients is due, among other things, to reduced availability of attentional resources and to poor encoding of actions to be performed.