AnxietyDiagnostic period Suspected breast cancer Uncertainty A possible diagnosis of breast cancer imposes a huge psychological impact on most women, but few studies have addressed uncertainty and anxiety changes at different diagnostic stages in women with suspected breast cancer. Thus, this longitudinal study examined uncertainty and anxiety and predictive factors for uncertainty in women with suspected breast cancer. Data were collected on uncertainty (Uncertainty in Illness Scale) and anxiety (State Anxiety Inventory) from 127 women at 3 times: upon notice of a breast biopsy, before biopsy, and after diagnosis. The results showed that uncertainty and anxiety levels were significantly higher before than after diagnosis. At the 3 data collection times, uncertainty and anxiety were significantly lower for participants diagnosed with benign tumors than for those with malignant diagnoses.Uncertainty and anxiety were positively, moderately correlated. Uncertainty was predicted by age, marital status, education level, religious status, family history of benign breast tumor, regular breast self-examination, self-perceived probability of receiving a breast cancer diagnosis, and biopsy result. Therefore, nursing professionals should be aware of the uncertainty and anxiety changes and impact of personal attributes on women with suspected breast cancer during the diagnostic period and provide care programs to alleviate their psychological distress. B reast cancer is the most common cancer and fourth leading cause of death among Taiwanese women. 1 Although newly diagnosed breast cancer patients account for only 8.4% of the total female cancer population in Taiwan, the incidence of breast cancer in recent years has become the highest among all cancers. 2 For Taiwanese women, the average onset age for breast cancer is 45 to 49 years, 5 to 10 years earlier than for Westerners. 2 During the