Aim: To explore what difficulties are faced by general practitioners (GPs) when trying to make a diagnosis of asthma in adults, and whether there are patient characteristics that influence this process. Methods: A qualitative study in which three focus group discussions were conducted with 18 GPs. Results: GPs were confident with the components needed to confirm a diagnosis of asthma but not with the use of spirometry. GPs said that time was an important factor - time to undertake the tests in their practice, and time to persuade the patient to engage in the diagnostic process including follow-up visits. Patients who were less willing to engage in this process were likely to be treated symptomatically. Conclusion: Continuity of care is important. A diagnosis of asthma seems to be more likely in patients with an ongoing relationship with their GP where both are willing to engage in the diagnostic process.