Background: Genetic and environmental factors are responsible for variations in the frequency of osteoporosis. Prevalence of osteoporosis in Mapuche women (native Chileans) is unknown. Aim. To assess the prevalence and risk factors for osteoporosis in Mapuche women. Material and method. A random sample of 95 asymptomatic postmenopausal Mapuche females, stratified by age, was studied. Women with diseases or medications that could interfere with calcium metabolism were excluded. Spine and femoral neck bone mass density was determined using a Lunar DPX Alpha densitometer. Results: Seventeen percent of women had normal bone mineral density in both spine and femoral neck. In the spine, 25.3% had a normal bone mineral density, 17.9% had osteopenia and 56.8% had osteoporosis. In the femoral neck, 34.7% had a normal bone mineral density, 57.9% had osteopenia, and 7.4% had osteoporosis. There was a positive correlation between bone mineral density and body mass index. Women with more than one hour per day of physical activity, had a significantly lower proportion of osteopenia or osteoporosis. No association between bone mineral density and parity or calcium intake, was observed. Conclusions: There is a high prevalence of osteopenia and osteoporosis among Mapuche women. Osteoporosis was associated with low body mass index (Rev Méd Chile 2002; 130: 1365-72).