This study examined (a) the prevalence and course of anxiety before the 1st 6 infusions of cancer chemotherapy and (b) the contribution of trait anxiety, side effect expectations, and prior occurrence of posttreatment side effects to anxiety before infusions. Fifty-three women receiving adjuvant chemotherapy for breast cancer participated. Anxiety was most prevalent and intense before the 1st infusion. Trait anxiety predicted anxiety before both the 1st and subsequent infusions. Prior occurrence of posttreatment nervousness also predicted anxiety before subsequent infusions, even after accounting for trait anxiety and other posttreatment side effects. Results are discussed in terms of the role that anxiety proneness, response expectancy, and classical conditioning may play in the development of anxiety before repeated chemotherapy infusions.