ABSTRACTIntroductionGiven the popularity of e-cigarettes, it is important to know who vapes, why, and whether different reasons for vaping are associated with vaping and smoking status.MethodsIn a UK cohort of young adults (23-26 years), we explored the characteristics of vapers and whether different reasons for vaping were associated with later vaping and smoking status. We used multinomial logistic regression to assess the association among ever smokers and vapers.ResultsEver and never vapers differed in numerous demographic and behavioural characteristics. Vaping out of curiosity was associated with lower likelihood of being a current vaper (adjusted relative risk ratio [aRRR] = 0.26, 95% confidence interval [95%CI] = 0.12 to 0.57, p < 0.001) but a higher likelihood of being a neither user compared to a current smoker at 24 years (aRRR = 2.13, 95%CI = 1.44 to 3.17, p < 0.001). Vaping to quit smoking was associated with higher likelihood of being a dual user (aRRR = 3.21, 95%CI = 1.74 to 5.90, p < 0.001) or a current vaper (aRRR = 3.26, 95%CI = 1.62 to 6.54, p < 0.001) but a lower likelihood of being a neither user (aRRR = 0.53, 95%CI = 0.34 to 0.82, p = 0.004) compared to being a current smoker at 24.ConclusionsIntention to quit smoking may be necessary for young people to effectively stop smoking using e-cigarettes.ImplicationsAlthough various studies have explored associations between reasons for vaping and both vaping and smoking, there is limited evidence from the UK. Particularly, evidence is limited among young adults as most research either focusses on adolescents or older adults. Among young adults in the UK, curiosity is a common reason for vaping but intention to quit smoking may be necessary for young people to effectively stop smoking by vaping.