Atypical diabetes mellitus (ADM) is characterized by severe hyperglycemia and unprovoked ketosis or ketoacidosis, with insulin resistance but with negative insulin-related antibody. The treatment of ADM firstly needs a short-term insulin therapy, which can be replaced by oral glycemic agent therapy or lifestyle intervention to control the blood glucose. ADM is regarded as a new subtype of diabetes different from typical type 1 diabetes mellitus and type 2 diabetes mellitus. In this paper, we reviewed the latest research progress on ADM, including its prevalence, clinical presentation, pathogenesis, diagnosis and management, hoping to help clinicians to better understand ADM and avoid the missed diagnosis and misdiagnosis.