An ongoing outbreak of lung injury associated with e-cigarettes or vaping (also known as E-VALI or VALI) started in March, 2019, in the USA. The cause, diagnosis, treatment, and course of this disease remains unknown. In this multicentre, prospective, observational, cohort study, we collected data on all patients with lung injury associated with e-cigarettes or vaping seen in Intermountain Healthcare, an integrated health system based in Utah, USA, between June 27 and Oct 4, 2019. Telecritical care, based in Salt Lake City, UT, USA, was used as the central repository for case validation, public reporting, and system-wide dissemination of expertise, which included a proposed diagnosis and treatment guideline for lung injury associated with e-cigarettes or vaping. We extracted data on patient presentation, treatment, and short-term follow-up (2 weeks after discharge) from chart review and interviews with patients undertaken by the Utah Department of Health (Salt Lake City, UT, USA). 60 patients presented with lung injury associated with e-cigarettes or vaping at 13 hospitals or outpatient clinics in the integrated health system. 33 (55%) of 60 were admitted to an intensive care unit (ICU). 53 (88%) of 60 patients presented with constitutional symptoms, 59 (98%) with respiratory symptoms, and 54 (90%) with gastrointestinal symptoms. 54 (90%) of 60 were given antibiotics and 57 (95%) were given steroids. Six (10%) of 60 patients were readmitted to an ICU or hospital within 2 weeks, three (50%) of whom had relapsed with vaping or e-cigarette use. Of 26 patients who were followed up within 2 weeks, despite clinical and radiographic improvement in all, many had residual abnormalities on chest radiographs (ten 67% of 15) and pulmonary function tests (six 67% of nine). Two patients died and lung injury associated with e-cigarettes or vaping was thought to be a contributing factor, but not the cause of death, for both. Lung injury associated with e-cigarettes or vaping is an emerging illness associated with severe lung injury and constitutional and gastrointestinal symptoms. Increased awareness has led to identification of a broad spectrum of severity of illness in patients who were treated with antibiotics and steroids. Despite improvement, at short-term follow-up many patients had residual abnormalities. Lung injury associated with e-cigarettes or vaping remains a clinical diagnosis with symptoms that overlap infectious and other lung diseases. Maintaining a high index of suspicion for this disease is important as work continues in understanding the cause or causes, optimal therapy, and long-term outcomes of these patients. Intermountain Healthcare.