Background: In this study, we determined the prevalence of and factors associated with parent unawareness of youth tobacco use. Methods: We used data from waves 1, 2, and 3 (2013-2016) of the Population Assessment of Tobacco and Health study, a nationally representative study of 13,650 US youth ages 12 to 17 and their parents. We conducted weighted multivariate analyses comparing parent unawareness of youth-reported ever use and associations between parents' unawareness of youth use and covariates. Results: Youth ever tobacco use ranged from 21.8% in 2013-2014, to 24.1% in 2014-2015, to 23.4% in 2015-2016. Parent unawareness ranged from 57.6% in 2013-2014, to 61.9% in 2014-2015, and 64.5% in 2015-2016. Factors associated with higher parent unawareness of youth tobacco use in 2015-2016 were youth being female, black, or Hispanic (adjusted odds ratio [AOR] = 1.24-2.61; all ps < 0.05). Youth with lower academic performance, relatives who used tobacco, tobacco available in the home, or past 30-day use, were less likely to have parents unaware of their use (AORs 0.33-0.56; all ps < 0.05). Conclusions: Among youth who reported ever using tobacco, most had parents who were unaware of their use. School-based efforts targeting specific sociodemographic factors could increase parent awareness of youth tobacco use.