- Background: Continuous positive airway pressure is the treatment of choice for patients with obstructive sleep apnea syndrome. Objective: To determine the factors influencing treatment initiation with a CPAP device in a healthcare system in which co-payment is required. Methods: A total of 400 adult patients with OSAS who required CPAP therapy completed questionnaires at three different stages of the diagnostic and therapeutic process: CPAP titration study (stage 1), patient adaptation trial (stage 2), and purchase of a CPAP device (stage 3). Logistic regression was used to analyze the variables influencing CPAP use at the different stages of the diagnostic and therapeutic processes. Results: Only 32% of the patients who underwent CPAP titration study purchased a CPAP device. The number of subjects who purchased a CPAP device increased gradually as monthly income increased, 28% vs. 62% in the "very low" and "very high" income levels respectively. Reporting for the titration increased in patients with excessive daytime sleepiness and an Epworth Sleepiness Scale score above 9 (odds ratio = 1.9, P = 0.015). Higher socioeconomic status increased reporting to stage 2 (OR = 1.23, P = 0.03) and CPAP purchase (stage 3, OR = 1.35, P = 0.002). Excessive daytime sleepiness increased reporting to stage 2 (OR = 2.28, P = 0.006). Respiratory disturbance index above 35 increased CPAP purchasing (OR = 2.01, P = 0.022). Support from the bed partner, referring physician and sleep laboratory team increased CPAP purchasing. Conclusions: A supportive environment for a patient with OSAS requiring CPAP is crucial to increase initiation of CPAP treatment. Minimizing cost sharing for the CPAP device will reduce inequality and may increase CPAP treatment initiation.