r Emergency presentation (EP) of cancer can be defined as the diagnosis of a new cancer as part of attending an emergency service such as Accident and Emergency, the Emergency Department or an Acute Medical Unit. r EP is common in lung cancer, affecting up to 40% of new diagnoses, and is a feature of healthcare in all countries. r EP of lung cancer is associated with specific patient demographics, such as older age and more co-morbidities, and certain disease characteristics including more advanced stage of disease. r Patients diagnosed via the emergency route are less like to receive anticancer therapy, and have a worse prognosis -especially 1 year survival -than those diagnosed through elective routes. r The emergency route to diagnosis may be unavoidable, and indeed the best option, for some patients. In that situation, prompt input from specialist lung cancer medical and nursing teams is essential. r The causes of EP of lung cancer are complex, and finding solutions is challenging. r Reducing EP of lung cancer may be achieved through development of streamlined diagnostic pathways, public health campaigns, provision of decision-support tools for general practitioners, better communication between primary and secondary care, and improved access to diagnostic oncology services. r Screening for lung cancer may have a positive effect on EP of lung cancer in the future.Asignificant proportion of lung cancer patients are first diagnosed as part of an emergency presentation (EP) to acute medical services. This route to diagnosis is a strong negative predictor of survival, and is associated with age, deprivation and medical co-morbidities. Patients are less likely to receive anticancer treatment than those diagnosed through elective routes. The causes of EP of cancer are complex. When it is unavoidable, prompt input from specialist lung cancer services is needed. Preventing EP of lung cancer involves streamlined diagnostic pathways, public health campaigns about symptoms, decision-support tools for general practitioners, improved communication and access for primary and secondary care, and focus on vague symptoms. Reducing EP of lung cancer is important when improving outcomes and patient experience.