Background Delaying a diagnosis of breast cancer directly and positively impacts survival. Self-efficacy has been shown to be a causal mechanism in a wide range of health behaviors, a measurable trait that predicts behavior across domains, which is strong associated with psychological variables. However, factors predicting self-efficacy of women with suspected breast cancer who delayed or did not delay seeking a breast cancer diagnosis over time have not been identified. Objectives To examine the differences between women who delay and women who did not delay seeking a cancer diagnosis, and key factors predicting self-efficacy over time among women with newly-diagnosed breast cancer. Design Descriptive, longitudinal design over 2 months following breast cancer diagnostic evaluation. Setting A medical center is located in southern Taiwan. Participants Eighty women with suspected breast cancer were approached and 67 subjects with a positive diagnosis of breast cancer were recruited. Methods Subjects were categorized into women who delayed their diagnosis and women who did not delay their diagnosis. A battery of 5 standardized questionnaires including self-efficacy, anxiety and depression, personality, spiritual support and hope was completed at the first three clinic visits. Results Stage of cancer, trait extroversion/neuroticism and spiritual support were significantly different between groups (p <0.05). Subjects who did not delay (β =−1.613, p <0.05), and time that histology results were provided (β =−2.4333, p <0.001) had a significantly predicted negative change in self-efficacy compared to the group that delayed. Hope at the first clinic visit contributed to the change in self-efficacy over time (β =0.391, p <0.001). Conclusions Personal factors affecting a woman's delay in obtaining medical assessment of breast cancer confirmation. Hope impacts self-efficacy of women with suspected breast cancer and interventions to enhance hope during the early stages of breast cancer evaluation require further study.