A major problem in the discussion of sleep-disordered breathing is caused by the use of different criteria to define its terms. Hypopnea is a good example of this: there is no consensus about its definition yet. In our study, the diagnosis value of apnea-hypopnea indexes (AHIs) determined by different hypopnea definitions was evaluated. The 90 patients who had an AHI > 5, scored according to the hypopnea definition of the American Academy of Sleep Medicine (AASM), participated in our study. The records of these patients were scored three times more according to different hypopnea definitions (hypopnea-arousal, hypopnea-desaturation, hypopnea-effort). AHI (AASM), AHI (arousal), AHI (desat), and AHI (effort) were determined via new scorings. Patients' daytime sleepiness was evaluated by the Epworth Sleepiness Scale (> 10). When all of three major symptoms (snoring, observed apnea, and daytime sleepiness) were found in a patient's history, the term "clinical OSAS" was applied. The Epworth value correlated with all of the indexes. In the scope of both the determination of daytime sleepiness and the verification of "clinical OSAS" diagnosis, the value AHI (AASM) = 5 had the highest sensitivity (100%) and specificity (94%).