The literature on self-care in people living with an ostomy pouch is expanding rapidly, yet a guiding theoretical framework remains lacking. This article aims to present the development of a situation-specific theory of self-care in people living with an ostomy pouch, encompassing both intestinal (colostomy and ileostomy) and urinary (urostomy) diversions. We describe the process of ostomy self-care, the key predictors of self-care behaviors, and their outcomes. Underlying assumptions and theoretical propositions are also outlined. Self-care includes actions directed toward maintaining the physiological stability of the stoma ( maintenance ), detecting complications ( monitoring ), and responding to them ( management ). Factors influencing ostomy self-care include self-efficacy and cultural context. Predictors of self-care may be sociodemographic, psychological, or clinical. Outcomes are categorized as clinical or psychosocial. A total of 9 theoretical propositions are proposed. This situation-specific theory offers a framework for understanding the multifaceted nature of self-care engagement in people living with an ostomy pouch. Future research should refine the theory by testing its propositions and assessing its applicability across diverse populations and health care settings.