Children with a mental illness may be at a significant risk of suffering from negative social evaluations and the exclusion of their peers. This paper examined healthy preschool children's earliest conceptual constructions of mental health and illness through two elected representations - the term crazy and depictions of emotionally and behaviourally deviant peers. Interviews with eleven preschool children reveal the concept of mental illness has yet to be constructed from a psychological standpoint. However, preschool children are highly sensitive to social-conventional as well as higher moral codes and discriminate against peers' who violate these codes, particulary those who display anti-social tendencies. Findings suggest that preschool is a formative period for establishing negative attitudes towards social and moral code violating behaviours that are often the symptoms of psychiatric conditions and which may represent the onset of more complex and enduring patterns of inter-group intolerance and discrimination. Implications for education are provided.