Introduction: Medical dental sleep appliance (MDSA) is an adjustable mandibular advancement device (MAD) recommended for treatment of snoring and obstructive sleep apnea (OSA). There are very few studies on Indian population which evaluate the therapeutic efficacy of mandibular advancement devices in the management of OSA. Materials and Methods: A prospective clinical study was carried out. Twenty polysomnography diagnosed OSA patients fulfilling the inclusion and exclusion criteria were treated with MDSA and changes in pre and post-treatment sleep para-meters (apneahypopnea index (AHI) and epworth sleepliness scale (ESS)) were recorded. Results: Mean differences in pre- (T₁ = 30.7 ± 5.0) and posttreatment (T₂ = 17.2 ± 3.9) AHI values and ESS pre-treatment (T₁ = 17.2 ± 0.6) and post-treatment (T₂ = 10.9 ± 0.9) were highly statistically significant (p < 0.001). Clinically the maximum improvement was observed in mild and moderate OSA cases. Although significant clinical improvement was also observed in severe OSA cases, the post-treatment AHI and ESS were still high. Conclusion: MDSA is a non-invasive, low risk and cost-effective treatment option for patients suffering from mild and moderate obstructive sleep apnea and also in cases of severe OSA who are not comfortable with CPAP or not willing for surgery.