Preventive medicine is supposed to be important for reducing bed-ridden ('netakiri', in Japanese) or frail elderly people. Previous studies showed that only about 30% of the bed-ridden elderly had decreased their ADL levels directly due to diseases, such as cerebrovascular disease or hip fracture. One of the other important causes of 'Netakiri' is disused syndrome. A few weeks after staying in bed, not only muscle power but also bone mineral density and intellectual interest often decrease in the elderly. Rehabilitation in daily life is expected to prevent disused syndrome. House-bound ('tojikomori', in Japanese) is supposed to be another cause of reduction of ADL. There are miscellaneous causes of tojikomori. Aging is one of the most important factors, but cannot be modified. Physical, mental, social or environmental factors are also important. Participation in social activity, improvement of intellectual interest and habitual physical excise, as well as prevention of diseases, is expected to be useful for preventing 'tojikomori' and 'netakiri' in the elderly.