The objective of this study was to identify the determinants of short hospital stay (< 24 h) among children admitted because of an acute asthma exacerbation. Computerized health records were used to identify children with a discharge diagnosis of asthma (ICD code 493.0) at the Hospital for Sick Children, Toronto, during the period October 1994 to October 1995. Cases were children with a length of hospital stay of < 24 h (short-stay group) and controls were children with a length of stay of > 24 h (long-stay group). Clinical and demographic data were extracted from the medical record. Over the 12-month period, 485 children were hospitalized because of asthma. Of these, 121 (25%) had short-stay admissions (< 24 h), whereas 364 (75%) had long-stay admissions (> 24 h). Simple random sampling was used to select 85 children from each of the two groups. There were no differences between the two groups regarding language, primary care physician, asthma history, management prior to emergency department (ED) presentation, respiratory rate on presentation, use of the observation unit, and time in the ED. Logistic regression analyses identified three variables associated with short hospital stay: milder asthma (adjusted odds ratio [OR] 4.9), male gender (adjusted OR 2.4), and availability of a delivery device at home (adjusted OR 2.0). In conclusion, many children admitted to hospital because of an asthma exacerbation have short, yet expensive, hospital stays. The results of this study highlight the importance of developing alternative models of health care delivery for asthmatic children requiring short hospital contact.