Since 1975 Laos has maintained a special relationship with Vietnam, formalized with the Treaty of Friendship and Cooperation signed in July 1977. Article 1 of the treaty states that "the two parties undertake to deploy all of their efforts to safeguard and develop the special relationship between Laos and Vietnam, to reinforce their solidarity and mutual confidence, their long-term cooperation and mutual aid in all domains in a spirit of proletarian internationalism." Article 4 of the treaty stipulates that "the two sides affirm their determination to build the Vietnamese-Lao border into a border of lasting friendship and fraternity."

The treaty is much more than its name implies, because it gives Vietnam almost carte blanche in the internal affairs of Laos, especially in the military. Vietnamese military forces have been continuously present in Laos since 1961, if not earlier. The strength of these forces has varied over the years from 30,000 to 50,000 troops in the 1975-83 period, to several hundred advisers in late 1987. In November 1988, the LPDR Ministry of Foreign Affairs formally announced that all Vietnamese troops had been withdrawn from Laos. Although Western intelligence sources initially doubted the claim of total withdrawal, later they reportedly confirmed that it was true. Indeed, there was no Vietnamese presence in the two border conflicts between Laos and Thailand in the late 1980s. Moreover, expatriate employees of international organizations working in Vientiane had noticed the removal of many Vietnamese technical and advisory personnel from the capital. It is likely that a full withdrawal of Vietnamese forces and a reduction of aid personnel occurred in order to advance economic agreements between Vietnam and China.

Vietnamese troops performed a variety of functions during their long stay in Laos. They fought alongside Pathet Lao insurgents in their struggle to overthrow the RLG. They trained and, along with the Soviets, equipped the military. Vietnamese cadres played a primary role in combatting the insurgency against the LPDR, undertaking security tasks such as guarding access to airport perimeters, controlling important road junctions, and patrolling sensitive areas. They performed border patrol duties and carried out joint military maneuvers with LPA units along the Cambodian, Chinese, and Thai borders to demonstrate strong Laotian-Vietnamese military cooperation. These maneuvers were especially evident during periods of border tension between Vietnam or Laos and their neighbors. The Vietnamese also rendered valuable engineering services such as building roads and improving infrastructure damaged by years of war.

Data as of July 1994