A retrospective survey was undertaken of children with difficult asthma, attending a respiratory clinic. The clinical and laboratory profiles of asthmatic children who were poorly controlled on > or = 800 microg of inhaled corticosteroids (ICS) were studied and compared to children well-controlled on > or = 800 microg ICS. Assessments were made of atopy, growth, lung function, treatment adherence, home environment, and responsiveness to corticosteroids (CS). Fiftyseven "difficult" and 23 well-controlled children were studied. Significant differences in the home environment were identified. Smoking was significantly more common in the difficult-to-control group. Nine children had alternative diagnoses. Poor CS responsiveness was present in 10 children. Adverse home environments, poor treatment supervision, alternative diagnoses, and unresponsiveness to CS were the most important factors in difficult asthma. A full assessment, including bronchoscopy, is indicated to avoid unnecessary increases in CS to doses that could cause side-effects.