We hypothesized that a "closed" intensive care unit (ICU) was more efficient that an "open" one. ICU admissions were retrospectively analyzed before and after ICU closure at one hospital; prospective analysis in that ICU with an open ICU nearby was done. Illness severity was gauged by the Mortality Prediction Model (MPM0). Outcomes included mortality, ICU length of stay (LOS), hospital LOS, and mechanical ventilation (MV). There were no differences in age, MPM0, and use of MV. ICU and hospital LOS were lower when "closed" (ICU LOS: prospective 6.1 versus 12.6 d, p < 0.0001; retrospective 6.1 versus 9.3 d, p < 0.05; hospital LOS: prospective 19.2 versus 33.2 d, p < 0.008; retrospective 22.2 versus 31.2 d, p < 0.02). Days on MV were lower when "closed" (prospective 2.3 versus 8.5 d, p < 0.0005; retrospective 3.3 versus 6.4 d, p < 0.05). Pooled data revealed the following: MV predicted ICU LOS; ICU organization and MPM0 predicted days on MV; MV and ICU organization predicted hospital LOS; mortality predictors were open ICU (odds ratio [OR] 1.5, p < 0.04), MPM0 (OR 1.16 for MPM0 increase 0.1, p < 0.002), and MV (OR 2.43, p < 0.0001). We conclude that patient care is more efficient with a closed ICU, and that mortality is not adversely affected.