Objectives: In this study, we assessed complete switching away from cigarette smoking among adult smokers who purchased a JUUL Starter Kit (JSK). Methods: Adult (age ≥ 21) established smokers (smoked ≥ 100 lifetime cigarettes) who purchased a JSK in 2018 were invited to complete online surveys 1, 2, 3, 6, 9 and 12 months after initial JSK purchase. Point prevalence of switching (no past 30-day smoking) was assessed at each follow-up. Repeated measures logistic regression models evaluated associations of sociodemographic factors, baseline smoking characteristics and time-varying JUUL System ("JUUL") use characteristics and switching across the 12-month period. Results: Respondents (N = 17,986) were 55.0% male, 78.3% white, mean age = 32.65 years (SD = 10.81), mean baseline cigarettes/day = 11.10 (SD = 8.16). The proportion self-reporting switching increased over time: one-month (27.2%[3718/13,650]), 2-month (36.4%[4926/13,533]), 3-month (41.0%[5434/13,257]), 6-month (46.6%[5411/11,621]), 9-month (49.4%[6017/12,186]), and 12-month (51.2%[6106/11,919]); 33.1% reported switching at both 9-month and 12-month follow-ups. In prospective analyses, smokers with lower cigarette dependence, shorter smoking history, lower cigarette consumption, more frequent JUUL use, greater satisfaction from initial JUUL use, and higher JUUL dependence were significantly more likely to switch. Conclusions: Rates of switching with JUUL increased over time. Over 50% of respondents reported complete switching away from cigarettes 12 months following purchase. Greater use of and dependence on JUUL predicted switching.