Obstructive sleep apnoea (OSA) is a potential cause of systemic hypertension in young and middle-aged people, and treatment helps reduce blood pressure in some patients. Severe OSA (apnoea-hypopnoea index [AHI] > 30/h) is strongly associated with increased mortality, stroke and cardiovascular disease in middle-aged populations. The cardiovascular risk from moderate OSA (AHI, 15-30/h) is uncertain, particularly if the oxygen desaturation index is low, although the data suggest an increased risk for stroke (particularly in men). There is no evidence of increased cardiovascular risk from mild OSA (AHI < 15/h). In the elderly, the cardiovascular risks of OSA are uncertain, although there is a likelihood of increased risk of stroke. Current, ongoing randomised controlled trials will inform whether OSA is a reversible cardiovascular risk factor within the next 5 years. Patients with cardiovascular disease, stroke, diabetes, obesity or poorly controlled hypertension are at high risk of OSA and should be questioned for symptoms of OSA, which, if present, may warrant further investigation and treatment. Weight loss has an unpredictable effect on OSA severity, but is independently beneficial for symptoms and metabolic health in OSA patients and is recommended for all overweight and obese OSA patients.