INTRODUCTION: Self-care is essential for health promotion, disease management and social justice. Robust, theory-based tools are needed for its measurement. The Self-care Inventory (SCI) was developed to measure self-care behaviours in adults regardless of their health status. The aims of this study are to measure validity of the SCI in an Italian sample and measurement equivalence in US and Italian samples. METHODS: We recruited 340 Italian and 294 US adults with convenience sampling. The Self-care Inventory, new General Self-Efficacy Scale, Positivity Scale, Perceived Stress Scale, and a clinical and sociodemographic questionnaire were administered online. Confirmatory factor analysis (CFA) was used to assess the factor structure of the SCI. Measurement equivalence testing was conducted using Multiple Group Confirmatory Factor Analysis, testing configural, metric, scalar, and strict invariance. For the Italian version of the SCI, reliability and construct validity were also tested. RESULTS: The SCI factorial structure was confirmed by CFA in the Italian sample. As for measurement equivalence, the Self-care maintenance scale demonstrated full metric and partial scalar invariance, indicating similar cognitive frameworks between US and Italian respondents. The Self-care Monitoring and Self-care Management scales achieved partial metric invariance. Reliability indices were satisfactory: Cronbach's alpha and Global Reliability Index ranged from 0.69 to 0.84, and test-retest reliability values ranged from 0.70 to 0.84. Construct validity was supported by significant correlations between SCI scales and measures of self-efficacy, positivity, and perceived stress. CONCLUSION: The SCI is valid and reliable for measuring self-care behaviours in the Italian population. Measurement equivalence show that SCI can be used cross-culturally and results from Italian and US samples are comparable. Our results support the use of the SCI in national and international self-care research and practice.