Cancer survivors often make health behavior changes in response to their increased risk for subsequent health problems. However, little is known about the mechanisms underlying these changes or whether they differ for positive and negative changes. This cross-sectional study applied a stress and coping model to examine both positive and negative health behavior changes in 250 middle-aged cancer survivors. A structural equation model showed that social support, sense of control over illness course, life meaning, and approach coping were related to positive health behavior changes; a lack of life meaning and avoidance coping were related to negative health behavior changes.