Brittle diabetes" was first used to describe a life "disrupted by episodes of hypoglycemia or hyperglycemia." Early descriptions focused on small case reports of mostly young women with psycho-social instability, recurrent diabetic ketoacidosis, poor patient compliance or maladaptation. We redefine "brittle diabetes" as occurring in four specific life stages each with distinct characteristics and associated conditions resulting in severely erratic glycemic control and poor outcomes. Once identified however these factors can often be reversed or significantly mitigated. The first group includes younger patients with associated psychiatric diseases such as bulimia and depression which require specific therapy and are treatable. A second group includes individuals who have another underlying medical condition resulting in disruption of insulin sensitivity or glucose utilization which must be sought. A third group, the largest we believe, has "geriatric type 1 diabetes" and develops severe glycemic instability due to frailty, chronic renal failure, dementia, vision loss, loss of counterregulation and other diseases of aging which lead to unintentional omission of insulin, insulin dosing errors and increasing insulin sensitivity. The fourth group, now seen around the world, suffers lack of insulin access and associated food insecurity. All four of these groups are described.