Postmenopausal women with breast cancer in remission (N = 140) who were participating in a randomized clinical trial of tamoxifen chemoprevention therapy completed measures of trait anxiety, symptoms, cancer worry, and breast self-examinations (BSEs) during the first 6 months of the trial. Trait anxiety was associated with heightened sensitivity to tamoxifen-induced symptoms (but not with tendencies to report increases in symptoms unrelated to tamoxifen use), greater tendencies to attribute symptoms to tamoxifen use, and greater cancer worry. Tamoxifen use increased BSE rates among high-anxiety participants. For low-anxiety participants, tamoxifen use increased cancer worry but not BSE rates. Trait anxiety appears to be associated with vigilant activation of illness-related representations that trigger attentiveness to sensations, worry, and protective coping in response to somatic cues.