Background: Studies on readmissions attributed to particular medical conditions, especially heart failure, havegenerally not addressed the factors associated with readmissions and the implications for health outcomes andcosts. This study aimed to investigate the factors associated with 30-day unplanned readmission for 10 commonconditions and to determine the cost implications.Methods: This population-based retrospective cohort study included patients admitted to all public hospitals inHong Kong in 2007. The sample consisted of 337,694 hospitalizations in Internal Medicine. The disease-specific riskadjustedodd ratio (OR), length of stay (LOS), mortality and attributable medical costs for the year were examinedfor unplanned readmissions for 10 medical conditions, namely malignant neoplasms, heart diseases,cerebrovascular diseases, pneumonia, injury and poisoning, nephritis and nephrosis, diabetes mellitus, chronic liverdisease and cirrhosis, septicaemia, and aortic aneurysm