In this study, the Cyclic Alternating Pattern (CAP) in the sleep stage 2 and in slow-wave sleep (SWS) of bipolar patients was compared to normal young adults. CAP is known to the EEG marker of arousal instability, whereas absence of CAP (non-CAP) relfects a condition of consolidated and stable sleep. Seven bipolar disorder patients, diagnosed by DSM-IV criteria, and age- and sex- matched normal comparisons were included in this study. Each participant underwent a polysomnographic overnight recording, after an adaption night. Sleep stages were scored manually, and CAP were scored by Somnologic program following standard criteria. Average spectra were obtained for each CAP condition from the signal recorded from C3/A2 or C4/A1, separately in sleep stage 2 and SWS, for each subject. The analysis of the relative power density in both groups showed that in sleep stage 2 and in SWS, CAP A1, A2, A3 subtypes had a higher power in all frequency ranges in normal comparisons than bipolar patients. Generally, A1, A2 and A3 showed clear spectral differences in both groups. CAP subtypes are characterized by clearly different spectra between bipolar and normal comparisons during sleep stage 2 or SWS. This study shows that bipolar patients who had sleep disturbance as a symptoms, are also characterized by clearly different by clearly different spectra and different power spectrum during sleep stage 2 and SWS.