AIM: To test the psychometric properties of the Self-Care of Chronic Illness Inventory (SC-CII) in patients living with inflammatory bowel disease (IBD). DESIGN: A cross-sectional, multicenter study. METHODS: A total of 452 IBD patients were recruited from nine centres across Italy. Participants completed the SC-CII, the Self-Care Self-Efficacy Scale (SCSES), and a sociodemographic questionnaire. Structural validity was assessed using confirmatory factor analysis (CFA). Reliability was evaluated with Cronbach's alpha and McDonald's Omega. Construct validity was determined through correlations between SC-CII and SCSES scores. RESULTS: CFA confirmed the SC-CII's structural validity, demonstrating its multidimensional self-care maintenance, self-care monitoring, and self-care management structure. Reliability scores were satisfactory, with robust internal consistency. Significant positive correlations between SC-CII and SCSES scores confirmed its construct validity. CONCLUSION: The SC-CII is a valid and reliable tool for assessing self-care behaviours in IBD patients. Its application in clinical and research settings can facilitate the evaluation of self-care practices, supporting the development of targeted interventions to improve patient outcomes. IMPLICATIONS FOR THE PROFESSION AND/OR PATIENT CARE: The SC-CII helps identify self-care deficits in IBD patients, enabling tailored interventions for better patient-centred care. IMPACT: The study addressed the need for validated tools to assess self-care in IBD patients, crucial for managing conditions like IBD. The SC-CII proved valid and reliable, with CFA confirming its structure and correlations with self-efficacy supporting validity. It offers a robust tool to assess and promote self-care behaviours. REPORTING METHOD: The STROBE checklist ensured accurate and comprehensive reporting. PATIENT OR PUBLIC CONTRIBUTION: IBD patients helped align the SC-CII with their experiences, ensuring its relevance. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT06015789.