Background: Recently, a relationship between autonomic nervous system dysfunction and fatigue was established. In Breast Cancer Survivors (BCS) it was demonstrated that heart rate variability (HRV) was lower in those who experienced high levels of fatigue compared to those who did not experience high levels of fatigue. It has been established that physical activity can normalize autonomic nervous system function in other populations. Hypothesis: High levels of physical activity and/or exercise tolerance will be associated with greater autonomic nervous system function and lower levels of fatigue. Methods: Nine women were recruited from the San Francisco Bay Area. Each participant completed the Aerobic Center longitudinal Physical Activity Questionnaire, a 6-minute walk test, and a body composition evaluation via BodPod. An electrocardiogram was collected during rest and during the cold pressor test (COLD) for HRV analysis. Five breast cancer survivors completed the Piper Fatigue Index. Pearson correlation coefficients were computed to examine the relationships between variables. All tests were considered significant at the 0.05 level. Results: BCS and controls did not differ in age, weight, height, total kcals/week of energy expenditure or blood pressure. During COLD lnLF and SDNN were greater in the control group (p < .05). Greater total energy expenditure and lnTPcold were negatively correlated (p < .05). Conclusion: This pilot study provides evidence for possible autonomic nervous system dysfunction in breast cancer survivors.