Sleep disturbances are frequently the consequence of physiological and psychological problems and may be classified in three groups: diminished total quantity of sleep, loss of the quality and inadequate timing of the sleep process. It is considered that one third of the population has a sleep disturbance some time in the life. Insomnia is the most frequent sleep disturbance but timely and careful diagnostic procedure is fundamental for the specific treatment. Factors connected with the increased prevalence of sleep disturbance are female gender, presence of mental or somatic diseases and advanced age. Sleep disturbances are classified in four basic groups: insufficient quantity or unrestorative sleep (insomnia); prolonged sleep (excessive daily somnolence or hypersomnia); problems with timing of sleep and problems close to or within the sleep process (parasomnias).