PURPOSE OF REVIEW: Obstructive sleep apnea in adults is diagnosed by an apnea-hypopnea index (AHI) above five (at least five apneas and/or hypopneas per hour of sleep). Though the definition of apneas has remained stable, the scoring criteria for hypopneas has varied throughout the years. There is even more evidence now that scoring respiratory events associated with arousals should be included in the diagnosis of obstructive sleep apnea, as these patients may benefit from treatment. RECENT FINDINGS: Recent studies, trials and meta-analyses have demonstrated that respiratory events associated with arousal are associated with symptoms, such as poor sleep quality and excessive daytime sleepiness. These arousal-based hypopneas have also been noted to carry a risk of hypertension and other adverse health consequences. SUMMARY: Requiring a 4% oxygen desaturation for hypopneas may miss patients that may benefit from treatment for obstructive sleep apnea. These patients are typically younger, nonobese, and women as they have been found to have respiratory events causing sleep fragmentation versus significant oxygen desaturation as compared with other populations.