['Emergency department (ED) crowding has been identified as a major threat to public health.', 'We assessed patient transit times and ED system crowding measures based on their associations with outcomes.', 'Retrospective cohort study.', 'We accessed electronic health record data on 136,740 adults with a visit to any of 13 health system EDs from January 2008 to December 2010.', 'Patient transit times (waiting, evaluation and treatment, boarding) and ED system crowding [nonindex patient length-of-stay (LOS) and boarding, bed occupancy] were determined. Outcomes included individual inpatient mortality and admission LOS. Covariates included demographic characteristics, past comorbidities, severity of illness, arrival time, and admission diagnoses.', 'No patient transit time or ED system crowding measure predicted increased mortality after control for patient characteristics. Index patient boarding time and lower bed occupancy were associated with admission LOS (based on nonoverlapping 95% CI vs. the median value). As boarding time increased from none to 14 hours, admission LOS increased an additional 6 hours. As mean occupancy decreased below the median (80% occupancy), admission LOS decreased as much as 9 hours.'] Does emergency department crowding predict admission length-of-stay but not mortality in a large health system?