The present study evaluated whether Pennsylvania's 2016 law requiring a retail license for the sale of e-cigarettes was associated with adolescent e-cigarette use.Data were drawn from the 2015-2017 Youth Risk Behavior Surveillance System. We examined the prepolicy and postpolicy change in e-cigarette use for the state with the retail licensing requirement (Pennsylvania) compared with control states (New York and Virginia).Results showed that e-cigarette licensing policy was significantly associated with e-cigarette use. E-cigarette use among Pennsylvania adolescents reduced by 5.2 percentage points in 2017 when compared with New York adolescents, and a corresponding 21.6% decrease from its baseline prevalence level in 2015. Similarly, there was a 7.4 percentage point decrease in e-cigarette use in Pennsylvania when compared with Virginia (30.7% relative decrease from the baseline prevalence).An e-cigarette retail licensing requirement may be a useful policy tool in reducing e-cigarette use among adolescents.