Diabetes mellitus is a worldwide epidemic affecting the health of millions of people. While type 1 diabetes (T1D) is caused by autoimmune destruction of the insulin-producing beta cells of the pancreas, type 2 diabetes (T2D) results from a combination of insulin resistance and beta cell insulin secretory defect. Clear definition and diagnosis of these two types of diabetes has been increasing more and more difficult, leading to the inclusion of a new category, namely double or hybrid diabetes (DD) that demonstrates symptoms of both T1D and T2D via the accelerator hypothesis. In this review, we discuss the worldwide prevalence of DD, its main physiological characteristics, including beta-cell autoimmunity, insulin resistance, and cardiovascular disease, the main risk factors of developing DD, mainly genetics, obesity and lifestyle choices, as well as potential treatments, such as insulin titration, metformin and behavioural modifications. Increasing awareness of DD among the general population and primary care practitioners is necessary for successfully treating this complex, hybrid disease in the future.