Glucocorticoids represent the most important and frequently used class of drugs in the management of many inflammatory and immunologic conditions. Beside these beneficial effects, glucocorticoids are also associated with serious side effects. Cushing's syndrome, adrenal suppression, hyperglycemia, dyslipidemia, cardiovascular disease, osteoporosis, psychiatric disturbances, and immunosuppression are among the most important side effects of systemic glucocorticoids. These side effects are especially noticeable at high doses for prolonged periods. Even in low-dose therapy, glucocorticoids could lead to serious side effects. The underlying molecular mechanisms of side effects of glucocorticoids are complex, distinct, and frequently only partly understood. This comprehensive article reviews the current knowledge of the most important side effects of glucocorticoids from a clinical perspective.