An examination of the seroprevalence of foot and mouth disease (FMD) virus was conducted in the Lao People's Democratic Republic (Lao PDR) from 1996 to 2005, using structured surveillance and abattoir-based studies. Under structured surveillance, seropositivity ranged from 65.7% (Vientiane Capital, 1996) to 3% (Houaphan, 2005) for cattle and buffalo; and from 2.8% (Vientiane Capital, 1998) to 0% in separate studies of pigs. In each study, species composition was significantly associated with seroprevalence rates. For abattoir surveys, the majority of samples (60.5%) came from Vientiane Capital (33.0%), Savannakhet (14.0%) and Champasak (13.5%) provinces. The overall proportion of animals testing positive for the presence of antibodies against the FMD virus was 18.7% (ranging from 50.8% in Vientiane Province to 1% in Phongsali). Generally, antibodies against serotype O were the most prevalent. Cattle and buffalo that tested as seropositive were significantly older than the seronegative animals (p < 0.00005). The overall proportional seropositivity was significantly different for different species, as was the case with the antibodies against serotypes O, A and Asia 1. Some 22% of cattle, 55% of buffalo and 23% of pigs demonstrated seropositivity but this varied significantly between provinces.