You can take a Vietnamese-plated motorbike between the countries of Vietnam and Laos. As far as we know you cannot take a Lao-plated bike into Vietnam unless you are the registered owner of the motorbike. The two countries share 6 international border crossings.
* Sop Hun / Tay Trang
The Northern-most border in between Muang Khua on the Lao side, and Dien Bien Phu in the Vietnamese side, we have been told that this border crossing is either not possible, or expensive, with a motorbike. The guys who we bought our motorbikes off of in Luang Prabang tried to cross the border here and were not permitted to exit Vietnam with them. We have also heard from other riders that when they rode to this border crossing the immigration officials tried to extort a large amount of money from them.
* Na Maew (Na Meo) / Nam Xoi
This border crossing near the Lao town of Sam Neua allows for taking Vietnamese-plated bikes in between countries. When exiting Vietnam you are required to pay US$20 for an ‘import form’ which is supposedly meant to be handed back to customs when you leave Laos with your bike. They also charge a very inflated price for a Lao visa (US$45). As of January 2015, the road on the Vietnamese side is in a terrible state, with very thick mud making the journey quite hazardous. Leave yourself plenty of daylight hours if trying to make this crossing.
* Nam Can / Nam Khan
In between the large towns of Phonsavan in Laos and Vinh in Vietnam, the Nam Can border crossing is open to international tourists. We met two guys in January 2015 who took their Vietnamese motorbikes from Laos back into Vietnam at this crossing with no problems.
* Nam Phao / Cau Treo
A convenient crossing point near Vinh and Lak Xao in Laos, we have also heard stories of people successfully crossing at this border. We have not met anyone who has done this personally though.
* Dansavanh / Lao Bao
This border crossing is not too far from the city of Hue in Vietnam. We have no credible information on the possibility of crossing the border with a motorbike at Lao Bao, although we have heard stories that it is possible. Personally we would not hesitate in attempting this border crossing ourselves.
* Bo Y / Ngoc Hoi
This border crossing is between the major towns of Attapeu in Laos and Kon Tum in Vietnam. It is a remote crossing, with the road on the Laos side being a beautiful mountain pass. Watch out for logging trucks on this road. We crossed from Laos into Vietnam at Bo Y with no problems. The border officials in Laos and Vietnam did not ask for any bribes, fees or extra money to cross. No one asked for the import permits that came with our bikes.