Significant changes in emergency department length of stay and case mix over eight years at a large Swedish University Hospital

•A change in case mix occurred, primarily with an increase in unstable patients.•Median for all crowding variables, except LOS, were stable over the study period.•Median LOS increased by an average of 9 min/visit/year.•Median LOS increased most among patient groups ≥ 80 years, unstable and admitted.•ED crowding seemed to high extent be related to lack of in-hospital beds. Describe the longitudinal development of crowding and patient/emergency department (ED) characteristics at a Swedish University Hospital. A retrospective longitudinal registry study based on all ED visits with adult patients during 2009–2016 (N = 1,063,806). Patient characteristics and measures of ED crowding (ED occupancy ratio, length-of-stay [LOS], patients/clinician’s ratios) were extracted from the hospital’s electronic health record. Non-parametric analyses were conducted. The proportion of unstable patients (triage level 1–2) increased while the proportion of admitted patients decreased. All crowding variables were stable, except for LOS, which increased by 9 min/visit/year (95% CI: 8.8–9.1). LOS for visits by patients ≥ 80 years increased more compared to those 18–79 (248 min vs. 190 min, p