Objective. The initial phases and transitional periods of sleep facilitate electroclinical manifestations of juvenile myoclonic epilepsy (JME). The period at the time of waking is identified in the different phases of sleep by cyclic electrophysiological oscillations, which in turn are synchronous with the spike-and-wave of multiple spike-and-wave activity of the electric crises seen in JME and other epileptic syndromes, This observation supports the theory of an alternating cyclical pattern (ACP) as the trigger of these discharges. Patients and methods. Following classical macrostructural and microstructural patterns of EEG sleep analysis, we investigated electrophysiological behavior in 13 patients diagnosed as having JME, and 5 persons of homogeneous epidemiological characteristics as controls. Results. In our study we observed that both groups had similar macrostructural sleep parameters. However, in patients prone to crises, these were concentrated in the first two hours recorded and showed no differences in sleep-waking transition or ACP of phase I sleep. These were significant when both periods were compared with the remaining NREM sleep. Conclusion. We conclude from this study that ACP is the microstructural element of sleep which modulates and permits classification of epileptiform anomalies, mainly in studies at the time of wakening [REV NEUROL 1998; 27:801-4].