Illnesses and injury during space flight pose risks both to crew health and to mission objectives during Space Exploration. These risks are minimized in multiple ways (e.g. selection criteria, preventative measures, flying appropriate hardware and procedures). However, there has recently been an identified need to quantify the relative risk and provide a means to address adequacy of proposed treatment given the difficult medical conditions imposed by typical space missions. The Integrated Medical Model (IMM) is designed to identify and quantify crew health risks during flight and to evaluate the effectiveness of in-flight mitigation strategies. To derive a quantitative measure of relative medical condition risks, IMM integrates terrestrial and space flight evidence bases to quantify probability and consequences of in-flight medical risks using Monte Carlo simulations. Utilizing well accepted scenario driven techniques such as probabilistic risk analysis as a guide, IMM generates a set of quantitative measures, such as mission time lost or changes in fitness for duty, and their underlying uncertainty to enable decision makers to make objective assessment of crew health and mission outcomes with respect to our current level of knowledge. This paper describes the conceptual structure of the IMM, including the processes for identifying and assessing likelihood of medical conditions, assessing and optimizing the resources to treat such conditions, quantifying health and mission impact from medical condition occurrences and means of validating and verifying the model.