This paper presents a discourse analysis of parents' talk about the knowledge, expertise and authority of professionals, during assessment and diagnosis of their child for an autistic spectrum disorder at a Child Development Centre. Focusing on the positional level of analysis, it was suggested that parents' constructions of professional expertise and authority were inherently ambivalent and at times contradictory. It was further argued that this ambivalence is also reflected in an ideological dilemma between equality and expertise, regarding the role and positioning of 'human relations experts'. Discourse analysis was found to be a particularly useful tool in investigating aspects of the parents' talk relating to authority, knowledge and expertise. It is suggested that acknowledging this ambivalence and scrutinizing one's assumptions and practice, rather than denying the authoritarian aspects of health care, would provide the basis for more ethical and respectful clinical practice.