Rapid eye movement (REM) sleep behaviour disorder (RBD) is a recently described parasomnia with important implications for diagnosis, treatment, and prognosis. Once thought to occur only in elderly males, it has now been reported in other groups including children and adolescents. The cardinal feature of RBD is the loss of REM atonia, which allows dreams to be acted out. Depending on the dream content, the accompanying behaviour can be dramatic, sometimes causing self-injury or harm to others. In adults, increasing numbers of associated conditions have been reported, notably neurodegenerative disorders of which RBD can be a prodrome. Other associations include narcolepsy, epilepsy, and antidepressant medications. Awareness that RBD can occur in young patients (admittedly rarely, it seems) is important. It is essential to distinguish between RBD and other dramatic parasomnias because each has different implications and treatment requirements. Children and adolescents displaying both clinical and polysomnographic features of RBD, and others with only polysomnographic evidence of loss of REM atonia, have been reported in association with various neurological and neurodevelopmental disorders. Reports of these cases are reviewed, together with suggestions for further reporting and research.