Individuals treated for cancer often experience higher levels of emotional distress than the general population. Previous research has shown that exercise can have an ameliorating effect on these problems. This 12-month prospective longitudinal study investigated mood, quality of life, cancer-related symptoms, and exercise behavior of 69 women who had completed treatment for Stage 0–2 breast cancer. We studied the natural progression of exercise participation after cancer treatment. Effects on mood, quality of life, and cancer-related symptoms were assessed after controlling for demographic variables, disease variables, social support, and baseline values to test the hypothesis that women who exercised were more likely to report better mood, higher quality of life, and fewer cancer-related symptoms. Results indicated that women did not increase their exercise participation over time and that overall mean minutes of exercise participation were below recommended levels. Baseline demographic predictors of exercise participation included younger age, having a spouse or partner, increased time since diagnosis, higher social support, and higher depression. Exercise participation was associated with improved physical functioning, but not overall mood or cancer-related symptoms. We discuss implications of these findings towards the well-being of breast cancer survivors. Copyright © 2002 John Wiley & Sons, Ltd.