As we expand the borders of traditional diagnostic nomenclature, distinguishing health from disorder becomes complex. This is especially true when the diagnostic lens views individuals as they exist within families that reside within wider social milieus. From this viewpoint, the recursive and interdependent factors influencing how individuals, relationships, and wider collectives contribute to and construe disorder need to be determined Systemic Cognitive-Developmental Therapy is one approach to conducting viable relational diagnoses and treatment, guiding therapists to formulate an understanding of the internal cognitive-developmental resources available to clients and other relevant, interdependent systems, and to examine the forces influencing the interactive discourse across these systems. The constructs of worldview, information processing styles, power differentials, and interpersonal connectiveness are presented as conceptual tools to guide relational diagnosis. An example illustrates relational diagnosis and treatment.