Objective: To test the psychometric properties of the Dutch 45-item Supportive Care Needs Survey—Partners and Caregivers (SCNS-P&C45-D) among partners of women with breast cancer living in the Netherlands. Methods: In this cross-sectional validation study, partners of patients with breast cancer were invited to complete a survey on the patient’s cancer and the caregiver’s level of unmet needs (SCNS-P&C45-D), psychological distress (HADS) and burden (EDIZ). Results: 43% of the invited informal caregivers responded (n = 302). Flooring effects were identified for three items of the SCNS-P&C45-D,which were then deleted from further analysis. The original factor structure and loading pattern of the SCNS-P&C45-D was not replicated. Internal consistency of the SCNS-P&C45-D and all subscales’ (emotional and relational needs, health care and illness related needs, practical needs, work and social needs) Cronbach’s alpha coefficients exceeded 0.80, the entire measure’s Cronbach’s alpha is 0.98. Most SCNS-P&C45-D subscales showed moderate correlations with distress and burden from informal care which was in line with expectations based on validity. The domain ‘Work and Social needs’ showed a high correlation with burden from informal care. Participants reported significantly more or higher unmet needs if they were younger (25.5% vs. 20.3% in older patients, p = 0.004), if diagnosis was less than 1 year ago in one subscale (Health Care and Illness related needs; 19.5% and 18%, p = 0.029, and the total SCNS-P&C45-D; 23.2% vs. 22.4%, p = 0.018). Conclusions: The SCNS-P&C45-D is able to identify those partners of patients with breast cancer in need and those who are not.