This thesis addresses two key questions: Do patients who attend a practice, where the Primary Health Care Team follow the 1993 British Thoracic Society (BTS) guidelines have a better quality of life, and do they have better controlled asthma? The study included 1065 patients and 169 partners from 37 practices. Practices were well equipped to manage asthma according to the BTS guidelines and GPs' knowledge and reported adherence was good, with the majority of partners reporting management decisions consistent with recommendations in the guidelines. 'Medication taken on home visits' (p=0.011) and 'the ratio of IHCS/β₂' (p=0.037) were statistically significant predictors of improved quality of life: Data were presented as mean scores per practice, therefore, my results predict outcomes that would improve for the 'average' patient; however, in the clinical setting, not all patients would benefit. Practice organisation did not impact on the relationship between guideline adherence and outcomes. The findings from this study have not convincingly demonstrated that guideline adherence translates into better patient outcomes. However, this is the first study to demonstrate an association between prescribing and patient outcomes in primary care. A better quality of life is observed in patients who attend practices with higher ratios of IHCS/β₂ prescriptions. This finding will be of interest to Health Authorities and Primary Care Trusts when planning performance indicators for the care of patients with asthma.