Despite literature indicating that expectations are important determinants of experiences of nonvolitional outcomes (e.g., pain, nausea), little research has explored their source. The dual process model suggests that concurrent experience of emotional distress should be a strong contributor, whereas social learning theory supports the position that expectations of nonvolitional outcomes should be based primarily on prior experience. These alternative hypotheses were tested in a sample of 80 breast cancer patients undergoing outpatient adjuvant chemotherapy, as such protocols provide a unique opportunity to study the impact of emotional distress and prior experience on patients' expectations of side effects. Bivariate analyses suggested that emotional distress contributed early in the course of treatment, but once prior experience of posttreatment nausea (PTN) was accounted for in the statistical model, distress no longer made significant contributions to patients' expectations of PTN, whereas prior experience did (p < .001). These findings suggest that experience of chemotherapy infusions is an important source of expectations for PTN, which may be representative of the source of expectations for nonvolitional outcomes in broader contexts.