This paper is an attempt to provide a critical evaluation of the theory of disability put forward by Lennart Nordenfelt. The paper is in five sections. The first sets out the main elements of Nordenfelt's theory. The second section elaborates the theory further, identifies a tension in the theory, and three kinds of problems for it. The tension derives from Nordenfelt's attempt to respect two important but conflicting constraints on a theory of health. The problems derive from characterisation of the (...) goals of persons; the difficulty which Nordenfelt has in respecting the plausible view that there is a distinction between illness and disability; and the presence in the theory of other strongly counter-intuitive implications. In section three a defence of Nordenfelt is attempted from within the resources available within his own theory. This defence seeks to exploit his distinctions between a person who is ill and one who is generally disabled and that between first- and second-order disabilities. However, it is concluded that there are insufficient resources within Nordenfelt's theory to fend off the criticisms developed in section two. The fourth section of the paper attempts a defence of Nordenfelt. It is claimed that introduction of the concept of capacity helps to explain differences between problem cases in the theory. Finally, it is shown that at least two important constraints on any theory of disability emerge from the preceding discussion. (shrink)