Response expectancies, defined as expectations for nonvolitional responses, have been proposed to contribute to the experience of side effects of cancer and its treatment. To statistically evaluate this association, a systematic search of the published literature was conducted, resulting in 14 studies appropriate for meta-analysis. Results revealed a significant (Z=6.58, P<0.001) medium-sized (r=0.36) association between patients' response expectancies for cancer treatment-related side effects and the experience of these side effects. Assessment of response expectancies with reference to the time the treatment-related side effect would occur resulted in larger effect sizes than when such temporal specificity in assessment was not included, Q(1)=10.27, P<0.01. Effect sizes were also moderated by patients' prior experience with cancer treatment, Q(1)=18.91, P=0.001, such that prior experience led to stronger associations between response expectancies and side effects than no prior experience. Relationships between response expectancies and pain, fatigue, nausea, and vomiting were explored. Effect sizes did not differ between side effects, with the exception that the relationship was significantly stronger for pain than for vomiting (P<0.05). Overall, these results support the contribution of response expectancies to cancer treatment-related side effects. Additionally, the results support the conduct of research on interventions to alter response expectancies, with the goal of reducing side effects and improving patient quality of life.