Abstract: This article explores some of the functions of psychiatric diagnosis and the implications this has for mental health nursing care. It critiques the psychiatric diagnosis as a categorisation process that maintains oppressive power relations within society, by establishing and enforcing normality through gender, culture and class biases. The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders is used to illustrate some of the inherent biases in the diagnostic process. The author argues that mental health nursing practice needs to demonstrate an awareness of the power relations inherent in any diagnostic process and make attempts to redress these at both the individual and sociopolitical levels. To create a true patient-centred partnership in mental health nursing, the nursing focus should be on the patient's experience rather than the psychiatric diagnosis with which the experience is attributed. NB this is a reprint of article first published in Journal of Advanced Nursing, 2000 Mar; 31(3), 583-9.