The first part of this essay is dedicated to outlining the desire theory of welfare. For this, I will contrast it with two other mainstream theories of welfare: the mental state account and the objective list account. I will then explain the challenges that each of the other accounts pose to the desire theory. In the second part, I discuss what is meant by harm and mental disorder. I will use George Graham’s concept of mental disorders. In part three, I will analyse why mental disorders are harmful according to the desire theory of welfare. I will show that the same flaws of the theory highlighted in the first section cause problems in explaining why mental disorders are harmful.