Severe mental illness can decrease life expectancy by up to 25 years and it is poorer physical health that causes this. Though the great majority of these excess deaths are smoking related, diabetes is also much more prevalent. We focus on diabetes because it is 2-3 times more common amongst those with poor mental health and has worse outcomes. Lifestyle factors are an important cause, but so is mental illness itself. Affecting motivation, memory and health literacy. Some medications can cause sedation and lethargy, increasing the risk of weight gain and poorer control of blood sugar. The problem is worsened by the various agencies not talking to each other, leaving patients who are struggling with poor mental health to self manage their illness but failing to provide the relevant support and education. Currently there are no UK studies solely on how to prevent, or self-manage diabetes for people with mental illness, or on how best to organise care. Our DIAMONDS research programme will find out who is at risk, what influences diabetes complications and what interventions will improve matters – both for individual patients and in terms of organising services. More high quality research is needed. Our research will also extend beyond the UK to South Asia where diabetes is a particular and increasing problem. We need to do far more to improve the physical health of people with mental illness. Finding more effective ways to prevent, manage and treat diabetes will be a key part of that effort.