Sleep disorders are an extra obstacle in the development and functioning of adolescents with psychiatric disorders. In spite of a good diagnostic interview it is difficult to obtain an objective judgement of the precise nature and seriousness of the sleep disorders. In ten adolescents, aged between 14 and 17 years, we produced hypnograms with ambulatory 24-hour cassette EEG recorders. This technique was successfully applied to these adolescents. The hypnogram made the diagnosis of the sleep disorders much clearer or provided important additional information. As a consequence it made the treatment more efficient and reduced the need for sleepmedication. The hypnogram, performed by ambulatory cassette EEG recording, greatly enhances the possibilities of good objective sleep research. In our opinion it is therefore an essential tool in the diagnosis of sleep disorders in adolescents with psychiatric disorders.