Background. In Vietnam, the cost of polygraphy or polysomnography for diagnosis of obstructive sleep apnea (OSA) is very high. Therfore, screening for OSA syndrome with small, inexpensive, and high reability device is requiered. Objective. To study the sensibility and specificity of respiratory event index (REI), measured by portable RU Sleeping in comparaison with apneahyponea index (AHI), measured by PSG (polysomnography), and in association with clinical symptom of OSA. Method. Subjects aged 25 or older living in Dalat city, having snoring3 nights/week, Epworth score 10, nycturia, morning headaches, daytime sleepiness had been included to perform RU Sleeping and PSG (Alice PDx) at the same time. REI index was used to compare with AHI in all study subjects. Results. 72 subjects were enrolled, including 38 male/34 female, mean age 49 + or - 2.4 years and BMI=26 + or - 8kg/m2. The cut-off point of REI for mild OSA was or = 10 (sensibility of 92 percent, specificity of 89 percent), moderate OSA: 32REI or =18 (sensitivity of 84 percent, specificity of 83 percent), and severe OSA: REI or = 32 (sensitivity of 92 percent, specificity of 88 percent). It was higher when REI or = 32 and history of awake sleep apnea. Conclusion. The diagnosis of OSA by RU Sleeping has a good value in the diagnosis of severe OSA when using REI index associated with clinical symptoms.