Sleep apnoea is a condition in which people stop breathing during sleep. A number of studies in general and worker populations have shown that the prevalence of an apnoea–hypopnoea index (AHI) >10 is in the range of 20%. Subjects with an AHI >10 that complain of excessive daytime somnolence, tiredness, asphyxic episodes during the night or non-refreshing sleep, among other symptoms, suffer from the sleep apnoea hypopnoea syndrome (SAHS). The prevalence of SAHS is around 4%. Owing to its high prevalence, clinical symptoms, probable secondary cardiovascular consequences and associated social problems, SAHS has a considerable impact on health, management of which is worth considering. Despite the fact that SAHS treatment has been challenged recent studies conclude that nasal continuous positive airway pressure (nCPAP) is undoubtedly effective in clearly symptomatic patients. Its use in clinical practice is adequately supported in the treatment of moderate to severe SAHS. Further studies are needed in order to define the lower range of symptoms to be treated. One of the most important problems encountered in this area results from the combination of two situations. On the one hand, different epidemiological studies have demonstrated that an AHI >10 without symptoms is present in around 15% of the general population. On the other hand, several studies suggest that having a high AHI, even without secondary symptoms, gives rise to some undesirable effects such as traffic accidents and cardiovascular consequences. In this context, comprehensive epidemiological studies are therefore warranted to define the role of nCPAP treatment especially in those subjects with a high AHI but with few or no symptoms.