Alcohol consumption is prevalent in late adolescence; however, little is known about its effect on sleep in this group. In mature adults, alcohol decreases sleep onset latency (SOL) and sleep efficiency (SE) and increases wake after sleep onset (WASO). It also increases slow wave sleep (SWS) and decreases rapid eye movement (REM) sleep in the first half of the night, with the inverse occurring in the second half. Alcohol's effect on sleep during late adolescence is of interest given that this age group shows both dramatic increases in alcohol consumption and significant developmental changes in the central nervous system. This study examined the effect of alcohol on sleep architecture in women and men aged 18 to 21 years and whether previously reported sleep architecture effects may have been as an artificial result of changes to sleep cycle length.