OBJECTIVES: The objective was to identify predictive factors and outcomes associated with patients who leave emergency departments (EDs) without being seen in Victoria, Australia. METHODS: This was a retrospective observational study of Victorian ED patient visits between July 1, 2000, and June 30, 2005, using linked hospital, ED, and death registration data. Index ED visits were identified for patients who left without being seen (LWBS) and for those who completed ED treatment and were discharged home. Statistical analyses included a general description and univariate analysis of patient, ED visit, temporal, and hospital-level factors. Logistic regression models were developed to assess risk factors associated with LWBS status compared to patients who completed treatment, to assess 48 hour re-presentations to ED; 48-hour hospital admissions; and 2-,7-, and 30-day mortality among those who LWBS compared to those who completed treatment. Adjusted odds ratios (ORs) and 99% confidence intervals (CIs) are presented. RESULTS: There were 239,305 LWBS episodes, for 205,500 patients over the 5-year period. Independent factors associated with LWBS patients in comparison to those who completed treatment include patients who are younger (15 to 24 years, OR = 2.46, 99% CI = 2.37 to 2.56), male (OR = 1.07, 99% CI = 1.05 to 1.08), of Australian indigenous background (OR = 1.63, 99% CI = 1.53 to 1.73), of non-English-speaking background (OR = 1.08, 99% CI = 1.06 to 1.10), noncompensable status (OR = 1.73, 99% CI = 1.68 to 1.79), self-referring (OR = 1.46, 99% CI = 1.43 to 1.49), nonassisted arrival mode (OR = 1.35, 99% CI = 1.30 to 1.40), and those with a hospital admission in the 12 months before the ED presentation (OR = 1.53, 99% CI = 1.51 to 1.55). Patients who LWBS had triage categories of lower urgency (nonurgent, OR = 8.21, 99% CI = 8.00 to 8.43), attended during the evening (OR = 1.10, 99% CI = 1.08 to 1.12), on either Sunday (OR = 1.20, 99% CI = 1.18 to 1.23) or Monday (OR = 1.20, 99% CI = 1.17 to 1.23), in winter (OR = 1.14, 99% CI = 1.12 to 1.16), with higher rates occurring in higher volume EDs (OR = 2.20, 99% CI = 2.15 to 2.26). There was no greater risk of mortality for LWBS patients compared to patients who completed treatment. The risk of hospital admission within 48 hours of discharge was lower for LWBS patients (OR = 0.60, 99% CI = 0.58 to 0.62); however, ED re-presentation risk was higher (OR = 1.63, 99% CI = 1.60 to 1.67). CONCLUSIONS: Patients who leave EDs in Victoria, Australia, without being seen are at lower risk of hospital admission and at no greater risk of mortality, but are at higher risk of re-presenting to an ED compared to patients who complete treatment and are discharged home.