Vitamin D insufficiency has recently drawn attention as a risk factor for osteoporosis. This paper evaluated vitamin D insufficiency in Japanese adults. The prevalence of vitamin D insufficiency, defined as serum 25-hydroxyvitamin D (25 [OH] D) concentrations less than 30 nmol/l, among independent community-dwelling elderly people was approximately five percent. Conversely, the prevalence of vitamin D insufficiency among frail, inactive elderly people with low levels of activities of daily living (ADL) was up to 50% greater. These results intimate that ADL may be an important determinant of vitamin D insufficiency. Overall findings highlight the need for measurement of serum 25 (OH) D to become a more common medical examination to detect vitamin D insufficiency in the elderly.