IntroductionUse of JUULs and e-cigarettes is growing rapidly, particularly among adolescents. Research suggests that flavours may increase the appeal of these products, but little is known about how flavours influence perception. We examined whether youth perceptions about the health risks of JUULs and e-cigarettes vary with flavours.MethodsWe conducted a national survey in 2018 of 1610 high-school students aged 14–18 who had ever heard of either JUULs or e-cigarettes. Respondents were asked to rate the lung cancer risk, the harm of second-hand vapour, potential for addiction and healthiness of differently flavoured JUUL and e-cigarette products. We investigated the relationship among flavour, risk perception and socio-demographic information.ResultsWe found that risk perceptions for both JUULs and e-cigarettes differ significantly by flavour type. Youths perceive fruit flavours to be less likely to lead to lung cancer (−0.909 (0.065)), have harmful second-hand vapour (−0.933 (0.060)) and be more addictive (1.104 (0.094)) relative to tobacco flavours. Candy, menthol/mint and alcohol flavours show similar patterns of risk association, although the magnitude is slightly smaller than for fruit flavours.ConclusionsYouths believe that flavours are related to the health risks of both JUULs and e-cigarettes despite the fact that these differences in risk by flavour have not been scientifically or systematically established. A policy concern is that misperceptions based on flavour may result in increased vaping by youths. The findings from this study support the assertion that banning fruit, menthol or mint and sweet flavours could reduce the appeal of JUULs and e-cigarettes to youth, with concomitant health protections.