Asthma is most common chronic respiratory illness worldwide, and makes up a large part of primary care practice. Family physicians need to be well-versed in asthma diagnosis, while avoiding overdiagnosis or misdiagnosis. The tetrad of cough, chest tightness, wheezing and dyspnea are conventionally thought to be the key presenting symptoms of asthma. However, these symptoms can occur in many other conditions, making accurate diagnosis of asthma challenging. This article aims to outline the clinical features and investigations that can help the family physician diagnose asthma and form possible differential diagnoses in adolescents and adults. Diligent history-taking remains paramount for diagnosis, while no investigation is definitive.