Interestingly the one charge that we normally consider fairly serious in Canada will not get you banned from the United States. We have many people who come to us requesting a US entry waiver for a DUI charge and we are forced to turn them away. Why? Because for some reason the United States does not consider DUI to be a crime of moral turpitude.
While I happen to disagree my thoughts on the matter are irrelevant in respect to United States law. So if you have a single DUI charge you most likely will not be refused entry when crossing the border.
On the other hand there is no guarantee that you will not be refused entry. We have several clients who were turned away who have nothing more on their record than a DUI. We don’t know exactly why that happened but it’s possible the border guard could see that the individual had been arrested, but could not see the nature of the offence. In a case like that I believe that most border guards would err on the side of caution.
Our suggest if you are travelling to the United States and there is a DUI on your record is to always travel with court documents or some other kind of proof of conviction. This way you can prove the nature of the offence in the event that the border guard believes there is reason to refuse you entry.