Improved management of very severely central nervous system (CNS) injured individuals has given rise to an increasing number of patients in a minimally responsive state. There is a growing literature stressing the importance of accurately determining these patients' level of cognitive functioning and its role in appropriate rehabilitation and long term management. The single case design model appears to be the intervention of choice, with its great flexibility and tailored approach to each individual case. The recent literature has focused on the technical aspects of the assessment, offering clear procedural guidelines. Unfortunately, there is a dearth of information about clinical factors such as clinical setting and family involvement, which may interfere with or prevent a planned intervention. The case of MT is presented, who was the subject of a single case intervention 9 months following an extremely severe traumatic brain injury. The planned intervention was to examine the effects of a psychostimulant on MT's level of arousal, in order to improve his participation in the rehabilitation programme. Beyond the results (which were equivocal), the clinical difficulties in conducting single case study designs in rehabilitation are discussed. Ways to minimize these difficulties are proposed.