CLINIC AND HISTORY: Expression of hypersomnia can take on several forms: long period of nocturnal sleep, excessive diurnal somnolence or both. History taking is essential. Useful tools include standardized questionnaires and a diary of sleeping habits. Not only do they provide evidence of the hypersomnia, but also information on possible eccentric origin(s). A pathological hypothesis can then be put forward: sleep apnea syndrome, narcolepsy, idiopathic hypersomnia, or periodic movements during sleep. POLYGRAPHY: Different recording protocols have been designed to determine sleep patterns, often depending on the clinical setting. The goal is to obtain an objective confirmation of hypersomnia and demonstrate a cause. The type of recording (hour and duration of the recording, parameters monitored) depends on the information desired. Because captors themselves sometimes perturb sleep, polygraphic explorations must be adapted to each individual situation.