The objective of this study was to determine whether the quality of asthma prescribing in general practice is associated with the severity of asthma patients' symptoms. Cross-sectional survey of asthma-like symptoms in patients prescribed antiasthma therapy was used. The setting was two general practices with contrasting ratios of corticosteroid to bronchodilator (high vs. low). The main outcome measures were: patient symptoms score and patient characteristics (age, gender, diagnosis, smoking, social class, and deprivation status). Patients on antiasthma therapy from the practice with the low corticosteroid to bronchodilator ratio had a higher mean symptom score (20.1, 95% CI 18.6, 21.7) than patients on antiasthma therapy from the practice with the high corticosteroid to bronchodilator ratio (13.2, 95% CI 11.8, 14.5). The mean difference in patient symptom score between the two practices was 7.0 (95% CI 4.9, 9.0); this changed little after adjustment for potential confounders. The quality of prescribing, as measured by the practice ratio of corticosteroid to bronchodilator, appears to be an important factor in the outcome of asthma care. The ratio of corticosteroid to bronchodilator in a general practice is one indicator of the quality of prescribing for asthma.