Introduction: Obstructive sleep apnea syndrome (OSAS) is a very frequent and underdiagnosed pathology with important social and economic implications. Continuous positive airway pressure (CPAP) is the gold standard for the treatment of OSAS, but adherence is low, with multiple factors being involved in this phenomenon. The purpose of the current study is to evaluate the causes of low adherence to CPAP among adults with OSAS and patients' symptoms. Materials and methods: We performed a prospective cohort study which included 95 patients admitted to Rosiori de Vede Pneumology Hospital, who were diagnosed with OSAS between January 2021-January 2023 and had indication to receive CPAP. Patients were divided into two groups (adherents and non-adherents) and were evaluated for one year based on completing a questionnaire and downloading data from the compliance card of CPAP on their regular visits at one month, six months and 12 months after diagnosis. Results:The predictive factors identified for non-adherence included oro-nasal mask use, low OSAS severity, low level of education, type D personality, high level of daytime sleepiness, and the first period of time with CPAP. Conclusion:Obstructive sleep apnea syndrome is a frequent and underdiagnosed pathology which benefits from CPAP as the gold standard treatment option. Although therapeutic results are favourable and effects are rapidly observed in symptomatic moderate-severe OSA, adherence to therapy remains low.