Objective: to clinically validate the defining characteristics of the “Caregiver Role Strain” Nursing diagnosis for caregivers of people in a palliative care situation. Method: a cross-sectional, quantitative, descriptive and analytical study. It was developed based on Fehring's Clinical Validation Model and on the diagnostic accuracy measures (sensitivity, specificity, predictive values and Receiver Operating Characteristic curve). The data collection instrument used was a form, applied in 2017 by two nurses to a sample of 111 caregivers of people in a palliative care situation, in Portugal. The caregivers were divided into two groups (with and without the diagnosis), being identified by the simultaneity of three criteria, namely: Zarit Burden Interview values greater than 56; agreement of two nurses about the diagnosis; and caregiver's perception of the presence of signs and symptoms. The defining characteristics were classified as major, secondary and irrelevant, according to the models used. Results: the prevalence of diagnosis was 42.3%. Of the 29 characteristics subjected to the validation process, 9 were considered major, 13 secondary and 7 irrelevant. Ineffective coping, depressive mood, frustration, worsening of previous diseases, stress and fatigue were the characteristics which proved to be more associated with the diagnosis in both analyses. The overall score of the diagnosis was 0.68. Conclusion: the study results contribute to the improvement of the diagnosis, making it more accurate. In addition, they enable better clinical decision in Nursing, allowing nurses to make a diagnostic judgment supported by scientific evidence.