It is important to identify patients with pneumonia because it is potentially a serious disease, often of bacterial origin, that should be treated with antibiotics. It is equally important to identify those with acute bronchitis, a self-limiting disease, that should not be treated with antibiotics. Because bacterial resistance is increasing, overprescribing of antibiotics should be avoided. However, it is sometimes difficult to differentiate between the two diagnoses, and guidelines concerning the assessment do not conform. Magnus Falk was my supervisor even during my GP training and encouraged me to continue the scientific research. During my PhD studies, I have come to realize how important it is to do pragmatic studies in a clinical context, especially in primary care, where most patients are managed, and where many have more than one disease.