To evaluate a Clinical Decision Unit (CDU) designed to utilize alternatives to emergency hospitalization. CDUs are one model of care designed to strengthen the gatekeeper role of Emergency Departments (EDs). This retrospective cohort study was carried out in a UK NHS acute hospital. All 854 patients in the CDU cohort were compared with three age-stratified, historical cohorts from the same clinical centre. The median age was 62 years (range 16-94).The main outcome measures were discharge to general practitioner, outpatient services or hospitalization, the 30-day unplanned reattendance rate for those not hospitalized, and monthly medical admission figures. Approximately 511 [59.8%, 95% confidence interval (CI): 56.5-63.1%] to 560 (65.6%, 95% CI: 62.3-68.7%) patients were admitted in the comparison cohorts, compared with only 186 (21.8%, 95% CI: 19.1-24.7%) in the CDU cohort (P≤0.05). Approximately 243 (28.5%, 95% CI: 25.5-31.6%) to 289 (33.8%, 95% CI: 30.7-37.1%) patients were discharged to general practitioner services in the comparison groups, compared with 562 (65.8%, 95% CI: 62.6-68.9%) in the CDU group (P≤0.05). Approximately eight (0.9, 95% CI: 0.5-1.8%) to 17 (2%, 95% CI: 1.2-3.2%) patients in the comparison groups were discharged to outpatient clinics, compared with 82 (9.6%, 95% CI: 7.8-11.8%) in the CDU group (P≤0.05). There was no consistent trend towards statistically significant rises in unplanned reattendance (P>0.05). Monthly medical admissions fell substantially during CDU operation. This CDU model was associated with statistically and clinically significant reductions in hospital admissions. The judicious application of this CDU model to other ED environments can be expected to yield similar benefits.