Obesity is the most important modifiable risk factor for obstructive sleep apnea (OSA). Lifestyle interventions that promote weight loss, including diet and exercise, are not expected to be sufficiently effective to improve apnea hypopnea index-based treatment outcomes in patients with OSA. However, they may be effective in preventing hypertension, lipid abnormalities, and cardiovascular diseases, which typically accompany OSA. Accordingly, lifestyle interventions and patient education are important for weight loss in obese patients with OSA. Additionally, positional therapy is a potential alternative treatment for patients who have difficulty starting and continuously using a continuous positive airway pressure machine. However, there remain no approved medical devices in Japan; moreover, the provided guidelines are only for educational purposes. Future studies are expected to confirm the effectiveness of positional therapy, and approved medical devices are expected to be developed in Japan.