The outcome of medical treatment in the intensive care unit (ICU) is a representative medical capability for hospital. Unscheduled readmission is regarded as an important indicator of quality in ICU. The unscheduled readmission rate does not only refer to medical quality but also refers to medical resources. In this article the guidelines for ICU admissions and discharges, the unscheduled readmission rates and effect factors will be introduced. (Tzu Chi Nursing Journal, 2004; 3:2, 26-30.)