Portrayals of characters with an intellectual impairment in nineteenth-century prose fiction are analyzed. In the earlier works idiocy is imprecisely differentiated from madness or eccentricity and the characters are mostly shown as socially and psychologically marginal and 'other'. In the later works a greater naturalism and a more precise notion of idiocy as a distinct condition is evident. Literary depiction of intellectual impairment or idiocy occurs in the seventeenth and eighteenth centuries but as an abstract condition; interest in the lives and personalities of people with an intellectual impairment is new to the nineteenth century. This, it is argued, is connected with a developing interest in ordinary people. The portrayals in the selected works are related to changing medical perspectives on idiocy and how it should be treated during the period, in particular to the publicizing during the eighteen forties of the view that idiocy could be ameliorated through education.