Sleep-disordered breathing a spectrum that ranges from snoring through disorder of increased airway resistance, to overt sleep apnea affects many clinical disease outcomes. Traditionally, disease outcomes have been measured by polysomnography, with the most common metric being the apnea hypopnea index (AHI). Multiple other clinical metrics are commonly used to assess the severity and impact of disease on important outcomes of obstructive sleep apnea (OSA). These allow assessment of sleepiness, quality of life, performance, and medical, especially cardiovascular outcomes. Currently the available metrics only partially explain the associated disease outcomes in different patients. This review highlights the available clinical, physiological and biomarker metrics in measuring OSA and associated co-morbidities and defines treatment goals.