INTRODUCTION Hospital readmissions are associated with increased healthcare expenses and with higher hospital fatality rates. We aim to characterize unplanned hospital readmissions occurred within 30 days after discharge, according to its Major Diagnosis Category, hospital type and location, and patients' demographic attributes. We also intend to estimate the hospital fatality rates associated to those readmissions, as well as to study the evolution of hospital readmissions rates in the last decade (2000-2008). Moreover, we aim to characterize heart failure readmissions. MATERIAL AND METHODS We analysed a database (provided by Autoridade Central do Sistema de Saúde) containing all hospital admissions occurred in Portuguese public hospitals. In order to compare readmissions rates, we performed chi-square tests and linear-by-linear association tests. RESULTS Between 2000 and 2008, there were 5 514 331 unplanned admissions, of which 4.1% corresponded to hospital readmissions, classified with the same Major Diagnosis Category of the first admission. Between 2000 and 2008, hospital readmissions rate increased continuously from 3.0% to 4.7%. Hospital fatality rate was significantly higher among readmitted cases (9.5 versus 5.6%, p < 0.001). Readmissions rates were also significantly higher among episodes involving older patients (2.6% in children versus 5.3% in the elderly) and males (4.5% versus 3.9% in females, p < 0.001), being lower in Lisbon region (2.7%) and in central hospitals (3.0%, p < 0.001). For episodes of heart failure, we found a readmissions rate of 6.7%. DISCUSSION AND CONCLUSION Most of the differences found are consistent with those described in other Western countries. Readmission episodes, whose rates have been increasing in Portugal, are associated with higher hospital fatality rates.