The purpose of this study was to identify factors for unplanned readmission within 15 days after discharge. We performed a retrospective case- control study on internal medical patients who were readmitted from a community teaching hospital from November 1, 2003 to March 1, 2004. There were 80 unplanned readmission patients enrolled. Another 80 patients who were not readmitted within 15 days after discharge were enrolled as control group. Research data were collected from the medical records and analyzed with multiple logistic regression. The result showed that patients with longer bed- ridden at discharge had higher risk of unplanned readmission within 15 days compared with those who were able to ambulate before discharge. The result indicates that it is necessary to monitor patients' bed-ridden days and increasing their mobility when providing discharge planning care training programs for caregivers to take care of patients after discharge are essential for avoid readmission.