Generally, a single arrest will not prevent you from getting U.S. citizenship but you may want to wait until 5 years have passed, after the case was dismissed, before applying. Applying earlier may impact the “good moral character” requirement. If you entered into a plea agreement where you had to do community service, pay fines, take random drug tests, attend an anger management class, etc., and the case was dismissed once you completed these requirements, this could be considered a conviction for immigration purposes. Applicants in this position could exercise wisdom by seeking the advice of an experienced immigration attorney before applying for U.S. citizenship.