The effects of age and gender on spectral characteristics of the waking EEG were investigated in a large sample of young adult men and women. In addition, relationships between spectral characteristics of the waking and sleeping EEG within an individual were explored. The sample included 28 females and 33 males in two age groups: 20-29 years (n = 32), and 30-40 years (n = 29). Spectral analysis was used to quantify EEG frequency characteristics for waking EEG just prior to sleep onset, as well as for the entire sleep recording. Significant effects of age were seen in the waking EEG but only in the delta frequency range (0.5-4.5 Hz) with lower delta activity in the older group (F = 11.6, P = 0.001). No significant gender effects were found in the waking EEG. Independent of age and gender, spectral profiles in the delta, theta, alpha and beta frequency bands of a subject's waking EEG were found to be highly correlated with their sleep EEG. In addition, subjects with high voltage alpha profiles during waking were found to sleep significantly longer and deeper than those with low voltage records. Significant correlations between waking and sleep EEG suggest that the spectral signature of an individual's EEG may be found across sleep/wake states.