Experiencing pain is a highly subjective feeling. Individuals who attend to persons in pain must often rely on inferences about that pain, since few measures are available to evaluate its real intensity. If pain is not clearly described, it will be incorrectly assessed and, consequently, poorly relieved. This problem is especially likely to arrive in patients with dementia or in patients with mental retardation who have difficulties in expressing clearly their feelings of pain. Special measures should be used to assess pain in these patients, or else their sense of isolation, already present because of their cognitive deficits, might grow deeper since behaviors associated with pain put a barrier between them and their surroundings.