This thesis consists of a number of collaborative studies aimed at the improvement of the diagnosis and care of children with diabetes mellitus. For the reader, who is not familiar with medical problems, a brief account is given of the clinical "behavior" of the disease ( 1) . It is perhaps clarifying to describe a disease as an entity which may display a behavior as if it were a living being. For non-medical people it sheds some light on the magic doctors seem to operate with. The many variables by which diseases may manifest their behavior imply that doctors, in caring for patients, constantly perform experiments. During a single week of active practice with a complex disease as diabetes, the clinician conducts more experiments than most of his laboratory collegues do in a year. The urge of some adolescents with diabetes mellitus to perform even more experiments at home, without their doctors knowing it, generates an even more lively behavior of this disease. In a psychologic or social sense, the word "behavior" refers to a person's attitude in various situations in life. In a more general sense, the concept of behavior applies to the interaction of an entity to its environment. With this concept, we can contemplate the behavior of a disease during its interaction with the human host (patient) , who provides the environment in which the disease conducts its "life". The disease can behave morphologically, to alter structures in the host's body. It can behave biochemically or biophysically to affect functions of the body. It behaves clinically, to produce symptoms typical for the host's illness, and psychologically as the host will counteract the impact the disease will exert on the host's life. This classification allows a summary of basic problems of childhood diabetes.