Animal and human studies have shown tolerance, consumption, relapse, and behavioral interactions between ethanol and nicotine, but little is understood about their interaction, especially as it relates to ethanol withdrawal in adulthood for subjects who have an adolescent history of using these drugs. This study investigated nicotine’s influence on ethanol withdrawal seizures in two different age groups of male C3H mice. Adolescent and adult male C3H mice, beginning at postnatal day (PD) 28 or 70, respectively, were subjected to a 7 day chronic exposure to ethanol only, ethanol plus nicotine, nicotine only, or vehicle treatment. Six weeks later, all groups were subjected to chronic exposure to ethanol vapors and the severity of their ethanol withdrawal seizures was assessed by handling-induced convulsions (HIC). An adolescent exposure to chronic nicotine resulted in an exacerbation of ethanol withdrawal seizures in adulthood. Given this, adolescence may contain a neurophysiological critical period that is sensitive to nicotine and which may result in an altered response to ethanol dependency in adulthood. These findings have serious implications for the long-term consequences following co-abuse of these drugs during adolescence.