Due to their anti-inflammatory and immunosuppressive properties, as well as their action on the hematopoietic system and the calcium phosphate turnover, corticosteroids are widely employed in the treatment of many diseases. However, the therapeutic use of these compounds is frequently associated with unwanted, mainly type A, effects that are directly dependent on the wide spectrum of their pharmacological activities. In this study these side effects are critically reviewed and classified on the basis of the organs and systems involved. Where possible, the incidence, pathogenesis, type of steroid, dose and schedule are reported, and the precautions that should prove useful in reducing the incidence and gravity of the side effects are given.