The clinical features of type 1 diabetes at diagnosis are almost entirely due to loss of functional islet beta cells and the resulting insulin deficiency. Abnormalities of glucagon secretion and hormonal responses to hypoglycaemia appear later in the natural history of the condition. Insulin resistance is not a prominent feature, although affected individuals may coincidentally be insulin resistant because of overweight or other reasons. The over-riding goal of treatment is therefore to replace endogenous with exogenous insulin, and to adjust insulin delivery to food intake and physical activity in such a way as to minimise deviations in circulating glucose outside the physiological range. Diabetes is a self-treated condition which makes great demands upon the individual and those closely involved in their lives. Effective practical training in diabetes management and education in its wider implications are therefore major priorities, but need to be introduced in a staged manner over time. Emotional and social support are badly needed, especially in the early stages, and normal responses to diagnosis – grief, anger, depression and denial – may be aggravated by adverse social circumstances. Practical issues such as driving, school or work need to be identified and dealt with promptly.