This study investigates the psychometric properties of the Adoption Communication Openness (ACO) Scale. Following a multi-informant approach, the study considered four versions of the ACO Scale to assess the child's perception of adoption communication openness with both mother and father and the mother's and father's perceptions of communication with the child. The validation sample included 331 Italian families, with an internationally adopted child (12-18 years). The factorial structure of the ACO Scale was evaluated through confirmatory factor analyses, leading to a mono-factorial structure with good reliability for all four versions of the scale. Evidence of full cross-relational invariance and partial cross-informant invariance was obtained, as well as convergent and criterion validity. Results confirmed the psychometric properties of the multi-informant ACO Scale in the Italian context and indicated it as a particularly suitable measure to investigate family members' perceptions of their levels of communication openness regarding adoption.