AIMS AND OBJECTIVES: To assess the level of nurse-to-nurse collaboration during the transfer of older people between hospital and primary health care and to evaluate the psychometric properties of the newly developed Nurse-to-Nurse Collaboration Between Sectors Instrument. BACKGROUND: Nurse-to-nurse collaboration is required when older people transfer between hospital and primary health care to enhance the safety and continuity of care to patients. There is a lack of evidence about the nature and level of this collaboration. DESIGN: A cross-sectional survey design was used. This study adhered to the STROBE checklist. METHODS: A sample of 443 nurses (university hospital n = 240, primary health care n = 203) participated in the study from October 2017 to June 2018. Nurses completed the Nurse-to-Nurse Collaboration Between Sectors Instrument (86 items, 7-point Likert-type scale), the Nurse-Nurse Collaboration Scale and the Patient-Centred Competency Scale. RESULTS: Nurses rated the overall level of nurse-to-nurse collaboration moderately high (mean=4.49, standard deviation=0.83, maximum 7.00). Nurses considered collaboration an important and confidential process, gaining older people's trust in their care. Lower scores were given to the agreement of mutual objectives, policies and guidelines in collaboration, opportunities for job rotation and interacting and networking during the collaboration process. The internal consistency reliability of the newly developed instrument was acceptable. CONCLUSIONS: Nurses collaborate with competence and confidentiality during the transfer of older people between care settings. However, there is a need for more opportunities to collaborate, to obtain mutual agreement about objectives, policies and practices, and better understand other nurse's roles and responsibilities in collaboration. The reliability and validity of the Nurse-to-Nurse Collaboration Between Sectors Instrument were acceptable though the number and wording of items will be reviewed and further tested. RELEVANCE TO CLINICAL PRACTICE: Nurses need opportunities to collaborate, and there is a need to develop agreed objectives, practices, roles and responsibilities in this collaboration.