Osteosarcopenia is a disorder consisting of concurrent osteoporosis and sarcopenia. This cross-sectional study using nationally representative data from Finland in 2000 aimed to determine the prevalence of osteosarcopenia in Finland. In addition, associations of sociodemographic, lifestyle, anthropometric, physical and mental function indicators, chronic conditions and various biomarkers with osteosarcopenia were examined. The study included 2142 subjects aged 55 and over (mean age 68.0years, SD 9.0). Probable sarcopenia was defined as grip strength < 27kg for men and < 16kg for women. Osteoporosis was defined as either ultrasound-based bone density measurement of T < -2.5, or self-reported, pre-existing diagnosis of osteoporosis. Participants were categorized into 4 groups: no sarcopenia and no osteoporosis, probable sarcopenia only, osteoporosis only, and osteosarcopenia. Information on sociodemographic, lifestyle, anthropometric, physical and mental function indicators, chronic conditions and various biomarkers were collected via structured interview, questionnaires, clinical examination, and blood and urine samples. The prevalence of probable sarcopenia, osteoporosis and osteosarcopenia was 13.8%, 11.1%, and 3.9%, respectively. Osteosarcopenia was associated with low BMI, slow gait speed, impaired mobility, impaired ability in the activities of daily living and depression. Of the two components, probable sarcopenia appeared to contribute to these associations more than osteoporosis. According to representative population-based study, about every fifth person with probable sarcopenia also has osteoporosis. Mobility and ADL limitations were more common among people with osteosarcopenia than those with osteoporosis or probable sarcopenia alone. Future studies are needed to examine osteosarcopenia as an independent risk factor for functional decline, hospitalization, and institutionalization.