Objectives: to establish whether there is a sub-group of patients suffering from senile dementia, Alzheimer-type (SDAT), who have ceased to undergo normal experience of pain. Methods: two single case studies are briefly described and a small-scale national survey by questionnaire is reported. Results: combining the original two cases with those garnered from the survey yielded 49 cases of SDAT patients who failed to exhibit normal experience of pain. In none of the cases does there seem to have been any particular problem of emotional expression or of verbal communication, but pain reactions to accidents, surgical procedures, infections and pre-existing conditions seem to have been extinguished. Conclusions: such patients may form a theoretically interesting sub-group with particular neuroanatomical pathology. Recognition of the existence of such a group has important legal and ethical implications for those treating or caring for patients of this kind.