This article summarizes the findings of an exploratory meeting of 53 experts brought together under the aegis of the Women's Health Initiative to identify important issues related to measuring physical activity in minority women, women in midlife (aged 40-75), and older women (aged > 75). The findings address five areas, three dealing with measurement and two concerning the design of surveys: (1) population characteristics to consider when measuring the physical activity of women and minority populations, (2) activity dimensions relevant to physical activity surveys, (3) measuring moderate and intermittent activities, (4) designing and administering physical activity surveys for older and minority women, and (5) establishing the reliability and validity of such physical activity surveys. Although the focus of the expert panel meeting was on identifying issues related to the measurement of physical activity in women, many issues summarized here can be generalized to children and men. The panel's findings concerning measuring physical activity are timely, as they directly bear on the challenges associated with the physical activity guidelines jointly issued by the Centers for Disease Control and Prevention and the American College of Sports Medicine and the recommendations made in the Surgeon General's 1996 report, Physical Activity and Health.