We surveyed the prevalence of parasitic infections in the mountainous province of Hoa Binh, north-west Vietnam, involving 526 households of six ethnic groups: Muong, Kinh, Dao, Thai, Tay and Hmong. Eggs or cysts of at least one parasite species were detected in 88% of stool samples (n = 2522). Prevalences of nematodes were high among all ethnic groups: hookworm (52%), Trichuris trichiura (50%) and Ascaris lumbricoides (45%). Ascaris infection appeared to be lower in households owning a latrine, was highest among children and decreased with age. Prevalence of hookworm rose during childhood, remained high until old age, was highest among adult women, but was not linked to anaemia. Eggs of Chlonorchis spp. were found in 126 (5%) individuals (of the Muong, Kinh or Thai groups only). Chlonorchiasis increased with age and was highest among adult men. Taenia eggs were found in three individuals (0.1%). Giardia lamblia was found in all districts and among all groups and the prevalence of infection was estimated at 3%.