STUDY OBJECTIVE: We evaluate the effectiveness and safety of an outpatient clinical care pathway for the initial treatment of acute proximal lower-extremity deep venous thrombosis (DVT) with low molecular weight heparin (LMWH) managed by the emergency department of 2 affiliated community hospitals. METHODS: This observational, retrospectively defined, population-based study with 39(1/2) months of preintervention analysis and 32(1/2) months of postintervention analysis was conducted in 2 suburban EDs of a large group model health maintenance organization. Our outpatient DVT clinical care pathway used careful patient selection and multidisciplinary follow-up. Ninety-six patients before the intervention and 178 patients after the intervention met eligibility criteria for the pathway. Adverse events during the first 2 weeks of treatment included symptomatic pulmonary embolism (PE), progressive DVT, minor and major bleeding, and death. RESULTS: Demographic and baseline clinical characteristics of the 2 groups were similar. Five (5.2%) of 96 preintervention subjects (95% confidence interval [CI] 2.4 to 8.1) developed adverse events compared with 5 (2.8%) of 178 postintervention subjects (95% CI 1.5 to 4.1; difference between groups 2.4%; P =.50). In each group, 1 (1.0% versus 0.6%) subject developed a PE, 2 (2.1% versus 1.1%) developed progressive symptoms of progressive DVT, and 2 (2.1% versus 1.1%) developed minor bleeding. Major bleeding occurred in 1 (1.0%) preintervention subject and no postintervention subjects. No patient in either cohort died. CONCLUSION: Managed by the ED, an outpatient DVT clinical care pathway using careful patient selection and an integrated multidisciplinary approach can provide a similar degree of effectiveness and safety as customary inpatient therapy.