We develop a systemic-organizational account of the notion of biological normativity and present the implications of this theoretical model for the medical practice. Sharing with authors as Canguilhem the rejection of the bio-statistical notion of clinical normalcy, we try to ground the theoretical notion of biological normativity considering it as an inherent feature of biological systems. In the first part, we present a critical survey of the understanding of this specific normative dimension from the main approaches in the contemporary philosophical debate on natural norms. In the second part, we develop a different account, based on the adaptive mechanisms of organisms, that avoids the limitations of the other stances and allows us to explain biological malfunctionality in terms of current organization. In our account, the organizational closure -i.e. the web of mutual constraining actions of the material structures on their boundary conditions that collectively self-maintain the whole organization of the system- provides a naturalized grounding of the concept of normative function from a systemic framework. Organizational closure constitutes the causal regime in which biological functions (or malfunctions) appear and can be identified. In the third part, we consider some significant medical examples showing how our approach is able to avoid the counterexamples and limitations of the predominant approaches in philosophy of medicine, such as Boorse's bio-statistical account. We claim that our approach provides the theoretical resources for a naturalization of the notion of biological normativity with relevant implications for a different naturalist conception of notions of health and disease.