Despite over 50 years of clinical experience, many uncertainties persist with respect to the onset of action, dose-response characteristics, duration of treatment, and optimal route of administration of systemic steroids when used in the treatment of severe acute asthma. Studies show that treating severe acute asthma with systemic corticosteroids within 1 hour of presentation to the emergency department lowers hospitalization rates and improves pulmonary function. The onset of action may be seen in as little as 2 hours in studies using peak flow, but may be delayed as much as 6 hours in studies using forced expiratory volume in 1 second as the pulmonary function outcome measure. A clear dose-response is seen at doses below 40 mg per day of methylprednisolone or equivalent; however, there is limited evidence for any added efficacy when doses above 60 to 80 mg per day are administered. There is no clear benefit of intravenous systemic steroids over oral steroids for treatment of severe acute asthma. High-dose inhaled corticosteroids may have a potential role, but further studies are needed to confirm efficacy. There is good evidence that a short course of oral systemic steroids for 3 to 7 days after initial steroid therapy prevents rebound asthma symptoms; no steroid taper is required if the patient was receiving inhaled steroids. Intramuscular steroids are at least equally effective and may be useful in patients who poorly adhere to their medication regimens; however, they are associated with more side effects than oral therapy.