ABSTRACT Objective: To investigate the effectiveness and adverse events of mandibular advancement device (MAD) in patients with obstructive sleep apnea (OSA) and to identify predictive clinical parameters for therapy success. Methods: A retrospective analysis of 318 patients indicated for MAD therapy, observed in a large teaching hospital in the Netherlands. Results: Ninety-seven patients (65.5%) achieved therapy success. A significant decrease in AHI (apnea–hypopnea index) and OSA-related symptoms was observed. None of the analyzed OSA-characteristics proved to be a significant predictive parameter for therapy success. Side-effects were reported in 54.4% of the patients, with temporomandibular dysfunction (27.0%) being the most frequent. Seventy-four patients (23.3%) discontinued treatment due to side-effects or therapy failure. Conclusion: MAD proved to be effective in the treatment of OSA and can be a viable alternative to CPAP in patients with severe OSA. Side-effects were relatively common and led to termination of therapy in 1 out of 10 cases.