Corticosteroids are adrenal hormones that play important physiologic roles including modulation of glucose metabolism, protein catabolism, alteration of calcium metabolism, regulation of bone turnover, suppression of immune system, and down-regulation of the inflammatory cascade. Because of their diverse effects, corticosteroids have been used therapeutically for treating a wide variety of auto-immune, rheumatologic, inflammatory, neoplastic and infectious diseases. In the field of pulmonology, corticosteroids have been used for the treatment of reactive airway diseases (such as asthma and allergic bronchopulmonary aspergillosis), chronic obstructive pulmonary disease, sarcoidosis, collagen vascular diseases (such as vasculitic disorders), eosinophilic pneumonitis, idiopathic interstitial pneumonias and infectious disorders (such as laryngotracheobronchitis). Different formulations of corticosteroids are commercially available including tablets, intravenous injections, intramuscular formulations and inhaled preparations. Long-term use of corticosteroids is often limited by their adverse effects, which include abnormal fat deposition, weight gain, diabetes mellitus, cataracts, glaucoma, osteoporosis, osteonecrosis, elevated risk of fractures, increased susceptibility to infections, proximal myopathy, depression, psychosis, adrenal atrophy with risk of Addisonian crisis, abdominal striae, acne vulgaris, delayed wound healing, easy bruising, electrolyte abnormalities and increased risk of peptic ulcer disease. As our understanding of corticosteroids advances, we may be able to identify individuals at higher risk of experiencing adverse effects.