The reporting of physical symptoms is influenced to a large degree by psychological processes. Individuals are more likely to notice subtle sensations in environments lacking in stimulation than those demanding external attention. The beliefs or schemas that people hold dictate where and how they attend to their bodies as well. These normal perceptual processes help explain why people are often poor at accurately detecting internal physiological activity. Several individual differences are also related to the symptom reporting process. Females are more likely to base their symptom reports on external situational cues than are males. In addition, individuals with chronic anxiety--those high in Negative Affectivity (NA)--report more symptoms than those low in NA. Finally, individuals, who have had traumatic experiences, either in childhood or within 1-6 months prior to a major symptom reporting episode, tend to be high symptom reporters. Several recommendations are made to help researchers and clinicians distinguish between psychological or perceptual factors with presumed biological effects. One implication of this work is that MCS and allied syndromes should be viewed as both a mental and a physical health problem.