Insomnia is defined as the inability to get the amount or quality of sleep necessary for optimal functioning and well being. Long term or chronic insomnia has been conventionally considered to be that lasting for at least 21 to 30 nights; however, it usually persists for months or years. It is more frequent in women than in men, and becomes more pronounced with age.Chronic insomnia is associated with mental disorders, psychophysiological conditions, inadequate sleep hygiene, neurological disorders and drug dependency. The most prevalent diagnosis is chronic insomnia associated with psychiatric disorders, followed in precedence by psychophysiological conditions.In chronic psychophysiological insomnia, idiopathic insomnia and insomnia associated with generalised anxiety, nonpharmacological strategies and sleeppromoting medication (e.g. hypnotics) are indicated. In patients with chronic insomnia associated with major depressive disorders, antidepressants that induce acute sedation (e.g. amitriptyline, doxepin, trazodone) represent the primary drug treatments of choice. When necessary, hypnotics can be added.Currently used hypnotics include benzodiazepine derivatives, the cyclopyrrolone zopiclone and the imidazopyridine zolpidem. Hypnotics with a short half-life show the best profile of efficacy versus adverse effects with regard to morning awakening and daytime functioning. In patients with chronic insomnia, hypnotics reduce sleep-onset latency, decrease the number of nocturnal awakenings and reduce the time spent awake. The increase in total sleep time is related to greater amounts of non-rapid eye movement (NREM) sleep.Few differences exist between benzodiazepines, zopiclone and zolpidem in terms of effectiveness in inducing and maintaining sleep. However, in contrast to the benzodiazepines and zopiclone, zolpidem does not suppress slow-wave sleep. Sleep laboratory and clinical studies tend to indicate that benzodiazepines are only effective when administered for relatively short periods of time in patients with chronic insomnia. Furthermore, a rebound insomnia has been described for short- and intermediate-acting benzodiazepines and zopiclone, and a withdrawal syndrome, denoting the presence of psychological and physical dependence, follows the abrupt cessation of benzodiazepine administration. In contrast, no evidence of tolerance or rebound insomnia has been observed in relation to zolpidem administration.