Insomnia, or the dissatisfaction with the quantity, quality or timing of sleep, is a common complaint. Because the definition of "normal" sleep is not well established, the estimates of the prevalence and severity of insomnia vary widely. Insomnia is often secondary to underlying psychiatric and medical conditions, and these should be evaluated and treated as a first measure. Nonpharmacological interventions for insomnia including sleep hygiene manoeuvres and exercise are recommended, although the success of these interventions has not been well documented. Benzodiazepines have been the pharmacologic agents of choice for the treatment of insomnia, but there is reason to exercise caution with their use; their overall benefit compared with placebo appears to be minor, and they are often associated with adverse cognitive effects. Unfortunately, no other class of drugs has proven to be superior to the benzodiazepines in terms of benefit:risk ratio. Given the importance of sleep for health and normal daily functioning the diagnosis, prognosis and treatment of insomnia should be a research priority.