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E-cigarettes have grown popular. The most common pattern is dual use with conventional cigarettes. Dual use has raised concerns that it might delay quitting of cigarette smoking. This study examined the relationship between long-term use of e-cigarettes and smoking cessation in a 2-year period.A nationally representative sample of 2028 US smokers were surveyed in 2012 and 2014. Long-term e-cigarette use was defined as using e-cigarettes at baseline and follow-up. Use of e-cigarettes only at baseline or at follow-up was defined as short-term use. Non-users did not use e-cigarettes at either survey. Quit attempt rates and cessation rates (abstinent for 3 months or longer) were compared across the three groups.At 2-year follow-up, 43.7% of baseline dual users were still using e-cigarettes. Long-term e-cigarette users had a higher quit attempt rate than short-term or non-users (72.6% vs 53.8% and 45.5%, respectively), and a higher cessation rate (42.4% vs 14.2% and 15.6%, respectively). The difference in cessation rate between long-term users and non-users remained significant after adjusting for baseline variables, OR=4.1 (95% CI 1.5 to 11.4) as did the difference between long-term users and short-term users, OR=4.8 (95% CI 1.6 to 13.9). The difference in cessation rate between short-term users and non-users was not significant, OR=0.9 (95% CI 0.5 to 1.4). Among those making a quit attempt, use of e-cigarettes as a cessation aid surpassed that of FDA-approved pharmacotherapy.Short-term e-cigarette use was not associated with a lower rate of smoking cessation. Long-term use of e-cigarettes was associated with a higher rate of quitting smoking.