Diabetes mellitus (DM) is a group of metabolic disorders of multiple etiologies characterized by hyperglycemia. In 2014 it affected approximately 422 million individuals worldwide. Unfortunately, it is associated with a set of co-morbidities that contribute to a significantly reduced, i.e. 5-10 years, life expectancy. The following review will discuss the most common long-term complications of diabetes. For practical reasons we decided to narrow our interests to its very widespread, even 90-95% of the cases, form - type 2 diabetes mellitus. During the discussion particular emphasis will be placed on the salivary glands function since previous investigation has confirmed its relation to many burdensome oral diseases, while the effective medical care over diabetic patients requires better understanding of pathomechanisms of its (i.e. diabetic) oral manifestations.