The category of common sleep disorders known as parasomnias includes disorders of arousal, rapid eye movement (REM) sleep behaviour disorder (RBD), nocturnal seizures, rhythmic movement disorder, and tooth grinding or ‘bruxism’. Parasomnias are all characterised as undesirable physical or behavioural phenomena occurring during the sleep period. Although these conditions can be distressing and, in some cases, hazardous to the sleeper and his or her bed partner, it is important to recognise that parasomnias are diagnosable and treatable in the vast majority of patients.Evaluation begins with a careful clinical interview with the sleeper and a family member to elucidate the frequency, duration, description and timing after sleep onset of these behavioural events.Disorders of arousal are the most common type of parasomnia and cover a spectrum from calm sleepwalking to emotionally agitated or complex behaviours, such as dressing or driving, for which the patient usually has no memory upon awaking. ‘Sleep terrors’ are quite common in young children and are often outgrown. Disorders of arousal represent a partial, as opposed to a full, awakening from deep non-REM sleep, typically occurring within the first 60 to 90 minutes after sleep onset.RBD is characterised clinically by a history of dream-enacting behaviour, and the patient may recall dream content. REM sleep periods typically occur in the latter half of the night. Physiologically, RBD results from a lack of the normal muscle atonia that is associated with REM sleep. RBD has been linked to a number of other neurological conditions; thus, a careful review of systems and a physical examination are crucial.A formal laboratory sleep study or polysomnogram with an expanded electroencephalographic montage can help distinguish among non-REM and REM parasomnias and nocturnal seizures. The latter may manifest clinically as arousals from sleep associated with vocalisation and/or complex behaviours.Rhythmic movement disorder can include head banging or body rocking at sleep onset or during the night. Tooth grinding is a common sleep-related behaviour that, when severe, can result in dental injury. Hypnagogic hallucinations (experience of dream imagery at sleep onset) and sleep-onset paralysis (experience of muscle/body paralysis as one is falling asleep) are symptoms rather than diagnostic categories. These phenomena classically occur in many individuals with narcolepsy, but also may occur in healthy sleep-deprived individuals.Safety precautions and good general sleep hygiene measures are recommended for individuals with a parasomnia, as the disorder can be exacerbated by sleep deprivation and various other factors. When the events are frequent or particularly dramatic, medication with a long- or medium-acting benzodiazepine, such as clonazepam, at bedtime is effective therapy in most cases of non-REM disorders of arousal and RBD. A dental guard may be helpful in tooth grinders. Relaxation training and guided imagery may be helpful strategies for some patients, especially those with disorders of arousal or rhythm movement disorders. There is no evidence of any association between parasomnias and psychiatric illness. Demystification of these conditions and reassurance, particularly for parents of paediatric patients, is an important aspect of clinical intervention.