Obstructive sleep apnoea–hypopnoea syndrome (OSAHS), obesity hypoventilation syndrome (OHS), periodic limb movement disorder and narcolepsy are the sleep disorders most commonly encountered in clinical practice. All four are characterized by sleep disturbance leading to daytime hypersomnolence. In OSAHS, repetitive partial or complete upper airway obstruction leads to respiratory effort-related arousals and sleep fragmentation. Weight loss can lead to resolution of symptoms. The mainstay of treatment is continuous positive airway pressure (CPAP).