ObjectiveWomen with breast cancer need to make difficult treatment decisions and may experience decisional distress (worry, anxiety, and thought intrusion) associated with these decisions. This study investigated ways that decisional distress was both associated with and distinct from other variables regarding decisional process and life functioning, and it investigated the validity of a decisional distress scale. MethodsA total of 263 women previously or currently diagnosed with breast cancer reported on initial treatment decisions regarding surgery, chemotherapy, or radiation, or decisions involving oral endocrine therapy (either currently or retrospectively). Participants completed online measures of decisional distress, alliance and confusion in patient-practitioner relationships, positive and negative interactions in close relationships, financial and general distress, and decision satisfaction. ResultsDecisional distress demonstrated a unidimensional factor structure invariant across treatment context groups, a wide range of meaningful variation, significant correlations with all hypothesized variables (especially patient confusion), but also key distinctions from other variables. ConclusionDecisional distress is a meaningful construct that can be assessed with precision, and important for understanding medical decision-making processes and patient quality of life. Practice implicationsAssessing decisional distress is crucial for evaluating treatment decision outcomes. One key to reducing decisional distress may involve reducing patient confusion.