Obstructive sleep apnoea (OSA) is a common condition. Whether an apnoeic patient should be considered for treatment depends on the definition of the syndrome, the rating of the severity and the potential morbidity associated with this condition. We have reviewed several types of evidence that early treatments of OSA deserved. There is a natural evolution of OSA leading to spontaneous aggravation and an increased cardiovascular morbidity in untreated patients in clinical populations. Excessive daytime sleepiness (EDS), the key symptom of the disease, can be found with very low apnoea hypopnoea index (AHI) and eliminated by adequate treatment. Cardiovascular risks are present with very low AHI and there is a high relative risk of developing hypertension in the future when patients present with mild OSA at baseline. The effect of treatment is significant when compared with placebo in the mildest forms of the disease. The clinical benefit, however, is mainly expected in terms of consequences for behavioural morbidity (i.e. reversibility of EDS and its related consequences) as the impact on cardiovascular morbidity is more doubtful and may anyway not be observed on a short-term follow-up. Overall, any OSA syndrome that is clearly responsible for EDS should be considered for treatment. Moreover, there is increasing evidence that the cardiovascular risk has to be taken into account when deciding on treatment, even in asymptomatic patients. All this evidence put together suggests early treatment in OSA.