The safety and effectiveness of "closed" intensive care units (ICUs) are highly controversial. The epidemiology and outcome of acute renal failure (ARF) requiring replacement therapy (severe ARF) within a "closed" ICU system are unknown. Accordingly, we performed a prospective 3-mo multicenter observational study of all Nephrology Units and ICUs in the State of Victoria (all "closed" ICUs), Australia, and focused on the epidemiology, treatment, and outcome of patients with severe ARF. We collected demographic, clinical, and outcome data using standardized case report forms. Nineteen ward patients and 116 adult ICU patients had severe ARF (13.4 cases/100, 000 adults/yr). Among the ICU patients with severe ARF, 37 had impaired baseline renal function, 91 needed ventilation, and 95 needed vasoactive drugs. Intensivists controlled patient care in all cases. Continuous renal replacement therapy (CRRT) was used in 111 of the ICU patients. Nephrological opinion was sought in only 30 cases. Predicted mortality was 59.6%. Actual mortality was 49.2%. Only 11 ICU survivors were dialysis dependent at hospital discharge. In the state of Victoria, Australia, intensivists manage severe ARF within a "closed" ICU system. Renal replacement is typically continuous and outcomes compare favorably with those predicted by illness severity scores. Our findings support the safety and efficacy of a "closed" ICU model of care.