Brittle diabetes is an uncommon complication of type I diabetes. However, the seriousness of the complication and its demands on the health care system warrant aggressive intervention. Studies during the last decade demonstrate that brittle diabetes is always secondary to a specific, identifiable etiology. This etiology is rarely apparent, however, without both extensive metabolic and psychological testing. In the long term, this testing is cost-effective inasmuch as approximately 50% of brittle diabetic patients are amenable to specific therapy. Several important issues have been clarified during the last decade, during which time major attempts have been made to understand the etiology of brittle diabetes. These issues may be summarized as follows: 1. There is always a specific etiology causing the brittle diabetes. 2. There are many different causes of brittle diabetes, but the most common are psychological abnormalities. 3. Therapy should always be directed at correcting the underlying pathogenic factor(s). 4. Empirical therapy and invasive procedures are contraindicated in brittle diabetic patients. 5. Extensive evaluation of a brittle diabetic patient may require referral of the patient to a diabetes center that has the expertise and manpower to appropriately evaluate a brittle diabetic patient. 6. Close follow-up and continued evaluation of therapy are necessary to confirm the suspected etiology and prevent diabetic ketoacidosis from developing. Unfortunately, only 50% of brittle diabetic patients respond to specific etiologic treatment. Research efforts during the next decade will focus on several clinical problems. First, improved psychological interventions are needed for common causes such as manipulative behavior and factitious disease. Second, treatment of severe systemic insulin resistance is still a major therapeutic challenge. Third, impaired glucose counterregulation needs to be better understood so that treatment is possible. The ultimate goal for physicians caring for brittle diabetic patients is to have effective therapy for all causes of brittle diabetes.