In alcohol-dependent individuals, synchronization of brain activity is different from that in non-alcohol-dependent individuals as reflected by EEG differences at alpha and beta frequencies (8-30 Hz). These EEG differences may not only be related to long-term alcohol intake but also to genetic factors that are associated with alcohol dependence. Thus, it is not known what the pure effect of long-term alcohol intake on synchronization of brain activity is. Therefore, we investigated whether EEG synchronization differs between light (0.5-6 drinks per week), moderate (7-20 drinks per week), and heavy (21-53 drinks per week) drinkers. All participants (49 males and 47 females) were free of a personal and family history of alcohol dependence. Eyes-closed EEG was recorded at rest and during mental rehearsal of pictures. EEG synchronization was determined by computing Synchronization Likelihood for six frequency bands (0.5-4 Hz, 4-8 Hz, 8-12 Hz, 12-20 Hz, 20-30 Hz, 30-45 Hz). Both male and female heavy drinkers displayed a loss of lateralization in alpha (8-12 Hz) and slow-beta (12-20 Hz) synchronization. In addition, moderately and heavily drinking males had lower fast-beta (20-30 Hz) synchronization than lightly drinking males. It is concluded that both male and female drinkers who drink 21 alcoholic drinks per week or more have impaired synchronization of brain activity during rest and mental rehearsal at alpha and beta frequencies as compared to individuals who drink less. As individuals with a personal or family history of alcohol dependence were excluded, the confounding effects of genetic factors related to alcohol dependence on synchronization of brain activity were minimized.