Asthma is usually easy to manage, but approximately 5% of patients are not controlled even on high doses of inhaled corticosteroids. It is important to assess these patients carefully in order to identify whether there are any correctable factors that may contribute to their poor control. It is critical to make a diagnosis of asthma and to exclude other airway diseases, particularly chronic obstructive pulmonary disease (COPD), and vocal cord dysfunction ("pseudo-asthma"). Poor adherence to therapy, particularly inhaled corticosteroids, is a common reason for a poor response. There may be unidentified exacerbating factors, including unrecognized allergens, occupational sensitizers, dietary additives, drugs, gastro-oesophageal reflux, upper airway disease, or other systemic diseases, that need to be identified and avoided or treated. Psychological factors may be important in some patients, but it is difficult to know whether these are causal or secondary to troublesome disease. Some patients have instability of their asthma, with resistant nocturnal asthma, premenstrual exacerbations or chaotic and unpredictable instability (brittle asthma). A few patients are completely resistant to corticosteroids, but more patients are relatively resistant and require relatively high doses of corticosteroids to control their symptoms (steroid-dependent). Some patients develop progressive loss of lung function, as in patients with COPD. Management of patients with difficult asthma should be supervised by a respiratory specialist and should involve careful assessment to confirm a diagnosis of asthma, identification and treatment of exacerbating factors, particularly allergens, and recording of peak expiratory flow patterns. A period of hospital admission may be the best way to assess and manage these patients. Treatment involves optimizing corticosteroids therapy, assessing additional controllers such as long-acting inhaled or subcutaneous beta2-agonists or subcutaneous, theophylline and antileukotrienes. In some patients, the use of immunosuppressive treatments may reduce steroid requirements, although these treatments are rarely effective and have side-effects. In the future, the nonsteroid anti-inflammatory treatments now in development may be useful in these patients.