INTRODUCTION Obstructive sleep apnoea (OSA) can be regarded as a condition characterized by repetitive upper airway obstruction leading to sleep fragmentation, cardiovascular stimulation and oxygen desaturation during sleep. These together lead to symptoms such as snoring, unrefreshing sleep, excessive daytime sleepiness (EDS) and the increased risk of cardiovascular disease, hypertension, insulin resistance and road traffic accidents. Any individual with time may oscillate within a spectrum of sleep disordered breathing, from intermittent simple snoring, to chronic heavy snoring, to upper airway resistance syndrome (UARS), to mild OSA, to moderate OSA, to severe OSA or to obesity hypoventilation syndrome (OHS). OSA is characterized by complete breath-holds (apnoeas) and partial breath-holds (hypopnoeas) – scientific physiological descriptions are presented in Chapter 73, Physiology of sleep and sleep disorders. With the present obesity epidemic, ear, nose and throat (ENT), hypertension, obesity, diabetes and sleep specialists are witnessing a large increase in the prevalence of OSA in their practice. This chapter describes the medical management of OSA, especially associated comorbidities, diagnosis and continuous positive airway pressure (CPAP), all relevant to the work environment of ENT specialists. Mandibular devices are not discussed in this chapter and are described in Chapter 75, The surgical management of snoring.