Sir: The Code of Practice (Department of Health & Welsh Office, 1999) sets out in detail the basic principles governing consent. It is clear from this that in order to understand the nature, purpose and likely effects of a treatment patients require some awareness of their diagnosis. The Patient's Charter for Mental Health Services (Department of Health, 1997) states that patients can expect “to be able to ask for an explanation of your diagnosis in plain language and to ask for more information if you do not understand”. This raises the question as to how much psychiatric patients know about their formally allocated diagnoses, with the implication this has for consent issues.

We conducted a questionnaire survey of out-patient and day hospital attendees, under regular psychiatric follow-up, with a view to considering this issue locally. An impressive knowledge of diagnosis was demonstrated by those patients suffering schizophrenia (72%, n=18), bipolar affective disorder (79%, n=14) and depressive disorders (89%, n=27). However, those with a primary diagnosis of personality disorder or substance misuse problems demonstrated considerably less awareness of this in their responses (with only 25%, n=24 and 42%, n=12, respectively). Whether this means that they have never been informed of the diagnosis, did not understand the explanation, are unable to recall it or choose to disregard it is unclear. However, if there is genuine ignorance among this group as to what it is that is being treated, then careful thought must be given to matters of consent. Are the patients consenting to the same thing as the treating psychiatrist imagines? Can you have informed consent in the absence of diagnostic awareness?