Treatment response of mild obstructive sleep apnea (OSA) to continuous positive airway pressure (CPAP) therapy and oral appliance (OA) is still controversial. The aim of this study is to evaluate the effect of CPAP and OA treatment on: objective and subjective sleepiness, cognitive deficits, mood changes, quality of life, inflammatory profile and metabolic cardiovascular and hormonal alterations in mild OSA subjects. Subjects with mild OSA (apnea -hypopnea index of 5 or more events per hour of sleep and less than 15), both genders, body mass index lower than 35Kg/m2 and age between 18 to 65 years will be included. They also must have a minimum mandibular protrusion of 7mm. Subjects will be randomly distributed in three groups: group 1 with CPAP, group 2 with OA and group 3 will be the control. At baseline evaluation, six months, one year and three years, all subjects will be submitted to sleep questionnaires, physical examination, ear-nose and throat evaluation, baseline polysomnography (and with CPAP for groups 1), Epworth Sleepiness Scale, Karolinska Sleepiness Scale, Stanford Sleepiness Scale, Maintenance of Wakefulness Test, Chalder Fatigue Scale, Neurocognitive testing, Beck Inventories of anxiety and depression, Functional Outcomes of Sleep Questionnaire (FOSQ), WHOQOL-BREF quality of life questionnaire, Short Form-36 quality of life questionnaire, questionnaire for sexual dysfunction, blood analysis for inflammatory, metabolic and hormonal evaluation, assessment of heart rate variability, 24 hour blood pressure monitoring and endothelial dysfunction. Sleep hygiene care was offer to three groups. Analysis mean and standard deviation will be used for descriptive statistical and a general linear model will be applied for analysis within groups on different time.