Glucocorticosteroids (GS) are a group of steroid hormones that regulate human physiological reactions of a wide spectrum of the necessities of life, such as growth, reproduction, immune and inflammatory reactions. Synthetic corticosteroids are commonly used drugs in inflammatory, autoimmune and lymphoproliferative diseases. However, steroids therapy is associated with the occurrence of many side effects, including metabolic disturbances. One of them is poststeroid diabetes. Several mechanisms are responsible for diabetogenic effect of GS, such as antagonistic action against insulin, increase of insulin resistance at the level of the liver, skeletal muscle and adipose tissue, impaired secretory capacity of the beta cells, effects on alpha cells leading to increase glucagon secretion, decreased the incretin phenomenon and gathering visceral fat. Disturbances in glucose metabolism induced by the action of GS are characterized by normal or slightly elevated fasting glucose and markedly postprandial glucose increase, especially in the afternoon and evening. Therapeutic efforts should therefore be directed at combating these particular disorders.