Objective To evaluate the value of Epworth sleepiness scale ( ESS) in evaluating the severity of obstructive sleep apnea hypopnea syndrome ( OSAHS) . Methods A total of 340 cases with suspected OSAHS were enrolled. The ESS scores and polysomnography ( PSG) monitoring data were analyzed. According to the PSG monitoring results the patients were classified into non-OSAHS, mild, moderate and severe OSAHS groups. The average ESS scores and the ratio of patients whose ESS score was ≥9 were compared among the four groups. The diagnostic value of ESS score was evaluated by ROC curve. The correlation of ESS scores with age, apnea hypopnea index ( AHI) , the lowest SpO2( LSpO2 ) and microarousal index was analyzed. Results The ESS scores had an ascending tendency as the severity of OSAHS was increased but only in the severe OSAHS cases the difference was significant statistically compared with the other three groups ( P lt; 0. 05) . The mean ESS scores in the four groups were 9. 96 ± 4. 81,10. 21 ±5. 48, 11. 48 ±5. 28 and 13. 52 ±5. 84, respectively. There was no statistical significance while comparing the ratio of patients whose ESS scores were ≥9 among the four groups. The analysis of ROC curve showed the area under the ROC curve ( AUC) was lesser( 0. 601) and a best cutoff could not be obtained. When ESS score ≥9 was made as the cutoff in screening OSAHS patients the sensitivity was 70. 0% and the misdiagnosis rate was 63. 21% . The ESS scores had positive correlation with the apnea hypopnea index ( AHI)( r =0. 240, P lt; 0. 01) and negative correlation with LSpO2 ( r = - 0. 198, P lt;0. 01) . The ESSscores had no correlation with age or the microarousal index ( P gt; 0. 05) . Conclusions The ESS score has some significance in screening severe OSAHS patients but can not exactly reflect the severity of OSAHS patients among Chinese population, suggesting ESS score has limited value in the evaluation of OSAHS severity. The ESS score ≥9 as a cutoff is not a reliable parameter to estimate the severity of OSAHS. A more effective scoring system need to be established for better screening of OSAHS patients.