The majority of adolescents do not obtain the recommended amount of sleep, resulting in significant daytime sleepiness. For most adolescents, insufficient sleep results from the interaction between intrinsic factors such as puberty and extrinsic factors such as school start times. Insufficient sleep and sleepiness impact all areas of adolescent functioning, including academic, psychological and behavioural, which underscores the importance of evaluating sleepy adolescents. While polysomnography is required for the diagnosis of certain sleep disorders, causes of sleepiness are generally best identified with a detailed sleep history and daily sleep diary. The management of sleep problems in adolescents involves treating any underlying sleep disorders, increasing total sleep time and improving other environmental factors that impact sleep. Recognition and management of insufficient sleep and sleepiness is important for the health and functioning of adolescents.