We review evidence that insomnia with objective short sleep duration is associated with physiologic hyperarousal; higher risk for hypertension, diabetes, neurocognitive impairment, and mortality; and with a persistent course. We propose that objective measures of sleep be included in the diagnosis of insomnia and its subtypes, objective measures of sleep obtained in the home environment of the patient would become part of the routine assessment and diagnosis of insomnia in a clinician’s office setting, and insomnia with short sleep duration may respond better to biologic treatments, whereas insomnia with normal sleep duration may respond primarily to psychological therapies.