The dissertation aims to study the relation between Nietzsche s answer to the mind / body problem and his concepts of disease and health. On this work, Nietzsche s interpreters will be divided in three lines of research: Metaphysics, Ficcionalist and Naturalist. We shall argue that Nietzsche s position about this issue is suspended between Ficcionalism (as is) and Naturalism (without metaphor) and that, consequently, it is difficult to identify his thought with Metaphysics. The argument that will be developed is that whilst Nietzsche is a monist, his monist points to a descriptive dualism: i.e., in order to express this identity, Nietzsche dualistically adopts a physiological / natural description as well as a psychological / fictional one. This position will be called Natural Ficcionalist Monism and we will try to show that it is correlated to physiopsychological concepts of disease and health.