Diabetes mellitus is one of the most common chronic diseases worldwide and is characterized by chronic hyperglycaemia. Despite the high prevalence of diabetes in the general medical setting and good evidence that mental health problems are common and reduce life expectancy, the development of diabetes-specific liaison mental health services is sporadic and piecemeal. This chapter begins by giving an outline of the clinical features of diabetes. Depression is the most common psychiatric disorder observed in diabetes mellitus. The particular clinical problems that occur when patients have both diabetes mellitus and an eating disorder have been highlighted in case reports. Psychiatric disorders are common in diabetes and are associated with poor diabetes control, complications and increased mortality. Diabetes is also an important complication of major psychiatric illnesses such as schizophrenia. There have been recent developments to identify specific psychological problems in diabetes such as depression, diabetes-specific fears and binge eating.