The best comprehension about the instability of the glycemia levels in type 1 diabetes mellitus (T1DM) patients and the availability of new alternatives to successfully control it, like insulin pump therapy and the insulin analogues, underlined the questions about the brittle diabetes existence as a clinical entity as well as the necessity of define it. The aim of this article was to describe the concept of brittle diabetes in the light of the latest advances in the treatment of type 1 diabetes and propose objective criteria to evaluate the level of glucose liability.