Diagnosis plays a significant role in the shaping of individual identities and the quality of life for people with learning difficulties and their family carers. Diagnostic labels are constitutive of peoples' lives, in that they bring forth pathology, create problem-saturated stories and construct careers as patients and cases. Disabled identities of people with learning difficulties remain largely 'embodied' and within the definitional control of professionals. Whilst the acquisition of a learning difficulty label can open doors to resources, it can also lead to disrespectful and dehumanising treatment, and the severe restriction of opportunities. This paper argues that a social constructionist perspective can offer a way of thinking about diagnosis that challenges the so called 'facts' and 'truths' that underpin and support it. Working in partnership with people with learning difficulties in relation to diagnosis requires professionals to relinquish power by resisting the 'temptations of certainty' associated with diagnostic practices.