Background: Although adherence to medical treatment is often posited as a pathway through which religion exerts its effects on health, this notion has rarely been examined. We assessed associations between dimensions of religiousness and adherence with medical advice regarding health behaviors relevant to their illness in a sample of 202 congestive heart failure (CHF) patients. We hypothesized that participants with higher levels of religious support and commitment and positive religious coping would have higher levels of adherence to health behaviors prescribed to manage their illness, whereas negative religious coping would be related to poorer adherence. Method: Participants were assessed through questionnaires twice over a six month period. Dimensions of religiousness assessed included religious social support, religious commitment, and positive and negative religious coping. Adherence was based on self-report and consisted of three factors measuring CHF-related behaviors, diet, and substance use. Results: Controlling for demographics, religious commitment was the sole predictor of adherence to CHF-related behaviors, an effect that remained when controlling for initial levels of adherence. No variables were related to adherence to diet. Religious social support and religious commitment were independently predictive of adherence to advice regarding substance use; the effect for commitment remained when controlling for initial levels of adherence. Conclusion: These results contribute to a small but growing body of literature indicating that facilitating adherence to medical regimens may be an important pathway through which religion exerts effects on physical health, particularly in those with chronic illness, but that the effects are specific to particular aspects of religiousness and behavior.