This research investigated the effects of health and environmental factors on the dropout and intermittent nonattendance of an exercise program designed specifically for older, female, primary-care patients living in the inner city. Class-attendance records (n = 21,538) from a cohort 110 women were analyzed. Women who dropped out early had poorer perceived health and were more likely to report pain as an exercise barrier at baseline. Those who lived in a census tract where a larger percentage of workers walk to work were less likely to drop out early. Intermittent nonattendance was associated with adverse weather conditions including heat index above 90 degrees F, wind-chill index below 20 degrees F, overcast sky, and snow. Better attendance was associated with greater atmospheric pressure, as well as lower number of sunlight hours per day. This research highlights the need to better understand environmental barriers when promoting physical activities in older women.