CPAP is effective in reducing symptoms of sleepiness and improving quality of life measures in people with moderate and severe obstructive sleep apnoea (OSA). It is more effective than oral appliances in reducing respiratory disturbances in these people but subjective outcomes are more equivocal. Certain people tend to prefer oral appliances to CPAP where both are effective. This could be because they offer a more convenient way of controlling OSA. Short-term data indicate that CPAP leads to lower blood pressure than control. Long-term data are required for all outcomes in order to determine whether the initial benefits seen in short-term clinical trials persist.