The close reciprocal relationship between sleep and mental disorders is clearly recognised today. Our findings, which have implications for early intervention, have suggested that puberty is the critical period for the development of insomnia symptoms and emergence of sex differences. In addition, our group has identified that sleep loss and deprivation are very common in Hong Kong children and adolescents, and are closely related to an array of mental and physical health conditions. These findings have subsequently been translated into a sleep education programme and delayed school starttime intervention. We also established the Sleep Assessment Unit (SAU) at Shatin Hospital, which provides both clinical service for local patients with sleep disorders and professional training to clinicians and technicians in sleep medicine from all over the world. The SAU is actively involved in epidemiological, translational and clinical studies in sleep disorders, as well as circadian rhythm disorders in various medical and mental disorders.