BACKGROUND: Inner city children make heavy use of accident and emergency (A&E) services for asthma. Developing strategies to reduce this requires a better understanding of the risk factors. METHODS: A case-control study was carried out of children with asthma living in south-east London: 1018 children who attended A&E for asthma over 1 year and 394 children who had not attended A&E for asthma over the previous year. The main risk factors were socioeconomic status, home environment, routine asthma management and parents' psychological responses to and beliefs about the treatment of asthma attacks. RESULTS: A&E attendance was more common in children living in poorer households. No associations were found with home environment or with measures of routine asthma care. Children who had attended outpatients were much more likely to attend A&E (odds ratio (OR) 13.17, 95% CI 7.13 to 24.33). Other risk factors included having a parent who reported feeling alone (OR 2.58, 95% CI 1.71 to 3.87) or panic or fear (OR 2.62. 95% CI 1.75 to 3.93) when the child's asthma was worse; and parental belief that the child would be seen more quickly in A&E than at the GP surgery (OR 2.48, 95% CI 1.62 to 3.79). Parental confidence in the GP's ability to treat asthma attacks reduced the risk of attending A&E (OR 0.30, 95% CI 0.17 to 0.54). CONCLUSIONS: There is no evidence that passive smoking, damp homes or poor routine asthma care explains heavy inner city use of A&E in children with asthma. Reducing A&E use is unlikely to be achieved by improving these, but identifying appropriate settings for treating children with asthma attacks and communicating these effectively may do so.