Hospital readmissions are common and expensive, and there is little information on the problem in Colombia. The objective was to determine the frequency of 30-day all-cause hospital readmissions and associated factors. This was a retrospective analytical cohort study of 64,969 hospitalizations from January 2008 to January 2009 in 47 Colombian cities. 6,573 hospital readmissions, prevalence: 10.1% (men 10.9%, women 9.5%), 44.7% > 65 years of age. Hospital readmissions was associated with higher mortality (5.8% vs. 1.8%). There was an increase in the Hospital readmissions rate in patients with diseases of the circulatory system. Hospital readmissions was more likely in hematological diseases and neoplasms. Mean length of stay during the first readmission was 7 days in patients that were readmitted and 4.5 in those without readmission. Greater total cost of hospital readmissions (USA 21,998,275): 15.8% of the total cost of hospitalizations. Higher prevalence rates in referred patients (18.8%) and patients from the outpatient clinic (13.7%). Hospital readmissions is common and is associated with longer length of hospital stay and higher mortality and cost. Increased risk of hospital readmissions in men > 65 years, patients referred from other institutions, and in hematological diseases and neoplasms.