This review will examine objective physiological abnormalities and medical comorbidities associated with insomnia and assess the need to measure parameters associated with these abnormalities for diagnosis and to monitor treatment outcomes. Findings are used to develop a decision tree for the work-up of insomnia patients. Currently available measures and those with possible future predictive value will be discussed. Costs, advantages, and the development of screening laboratory tests will be presented. It is concluded that there is a need to differentially evaluate insomnia patients based upon their comorbidities and the presence of objectively decreased total sleep time to direct optimal treatment. The development of objective diagnostic criteria and treatment outcome goals beyond subjective symptomatic relief will establish insomnia as a true medical problem and improve patient care.