Our aim was to develop an age scale for the assessment of functional fitness in older women. The subjects were 430 older Japanese ambulatory women. They were divided into three groups: (a) less active (N=373, age 72.5+/-6.7 years); (b) active (N=23, age 71.0+/-5.4 years); and (c) sedentary (N=34, age 72.9+/-4.7 years). The less active group was used for the development of the instrumental activities of daily living (IADL) age equation, while data from active and sedentary groups were utilized for the assessment of the criterion-related validity. Seventeen functional fitness variables were selected as test items related to IADL. IADL were defined as extra activities people engaged in during daily living, such as preparing meals, housecleaning activities, and washing. After applying the first principal component analysis to the correlation matrix among the 17 items, the following IADL age equation was obtained: IADL age = - 0.43X1 - 0.57X2 - 0.32X3 + 0.37X4 + 0.37CA + 61.88, where X1 = arm curl (n / 30 s), X2 = moving beans with chopsticks (n / 30 s), X3 = functional reach (cm), X4 = walking around two cones (s), and CA = chronological age (years). The mean IADL age of the less active group (72.2+/-8.4 years) obtained from this equation was matched with their mean CA. The mean IADL age of the active group (66.0+/-3.2 years) was significantly lower than their mean CA (71.0+/-5.4 years, p<0.05), and the mean IADL age of the sedentary group (79.1+/-6.0 years) was significantly higher than their mean CA (72.9+/-4.7 years, p<0.05). In conclusion, the criterion-related validity of the IADL age equation was clearly demonstrated as a means to assess the functional fitness required for IADL in older Japanese women.