Parental interference in judicial proceedings for variation of custody arrangements is a phenomenon that profoundly impacts family dynamics and the well-being of children. This article addresses this issue from the perspective of forensic psychological assessment, highlighting the critical importance of a thorough and rigorous analysis in these contexts. Custody variation, whether physical or legal, often generates tension and conflict between parents, which can lead to parental interference behaviors. These interferences can manifest themselves in a variety of ways, including emotional manipulation of children, denigration of the other parent, and obstruction of parenting time. The relevance of this article lies in the need to understand how these interferences affect both the children and the adults involved, and the importance of having accurate and objective psychological assessments to inform court decision-making. The work of the forensic psychologist is essential in these processes, providing an unbiased assessment based on standardized techniques and tools to identify harmful family dynamics and their impact on the psychological well-being of children. Throughout this article, the importance of early intervention and the implementation of effective strategies to mitigate parental interference is highlighted. In addition, recommendations for courts and other legal professionals on how to appropriately integrate findings from psychological evaluations into judicial decision making are highlighted. Ultimately, this approach seeks to promote the well-being of children and ensure that custody decisions are based on the best interests of the child, informed by rigorous and detailed forensic psychological evaluations.