As recently as the early 1990s, you had to get special permission to visit any province other than Vientiane, reporting to immigration on arrival in every new province and getting the required rubber stamp. This "reporting in" procedure - jaeng khao - has now been officially done away with throughout the country. However, there is no telling if and when word from above will bring new vigour to the old rubber-stamp game, so always check with other travellers. If in doubt, seek out the local immigration office, if there is one, or the police station.