A theoretical basis for the diagnosis of nursing problems, centered on the concepts of role insufficiency and role supplementation, is offered. Role insufficiency is anticipated and experienced by clients during role transitions with developmental, situational, and health–illness implications. The conceptual basis of nursing intervention is role supplementation, and components, strategies, and processes of role supplementation are described. Conditions that predispose clients in the health setting to undergo role transition, conditions under which aspects of role transition may become nursing problems, and the role of the nurse in dealing with clients' role transition problems are described. A predictive and prescriptive paradigm, showing the interaction of construct components, is presented.