Mental health variables must be related to health outcomes so that their usefulness can be demonstrated in health care settings. In the previous chapter, we explored how mental health variables commonly coexisted with physical illness variables, and in this chapter we will explore whether one mental health variable, cognition, affects a variety of health outcomes. For the clinician, the data provided here can be used to demonstrate the important linkages that cognition has with health outcomes. Cognition represents a direct measurement of a patient's level of performance, and in the context of a cognitive assessment can represent an indirect measure of a patient's brain functioning. Since cognitive impairment is so common in geriatric health care patients, the main role of cognition as a predictor is its sensitivity to brain dysfunction and decline in cognitive abilities.