To assess the quality of the information included in the minimum basic data set (MBDS) of the eight public hospitals of the Murcia region in order to ascertain what should be improved to be valid and reliable. An external encoder performed a recoding of a random sample of hospital discharges, using the patients hospital records and comparing afterwards the information obtained with the one reflected in the MBDS databases. Quality was assessed using 12 criteria. The reviewed discharges sample consisted at least of 96 cases per hospital (Type I error = 0.05, Type II = 0.10, for the most unfavorable case). A total of 796 cases were reviewed. The MBDS disagreement percentages with the patient record data were higher for the clinical data, with 41.6% for the main diagnosis and 33.5% for the main surgical procedure, being in both cases higher in those hospitals that had used to codify just the discharge record with regard to those that did so with the complete patient record. The variation rate in the diagnosis-related group (DRG) assignment was of 29.6%, and there was a decrease in the case-mix index of 1.07397 when reviewing with the patient record to 1.05555 in the MBDS. Within the administrative data, the highest disagreement rate was for the physician that signs the discharge (60.5%) and the patient's address (31.6%). In many of these assessed aspects there are significant differences between hospitals. A reliability problem was identified in the collected data, which mainly affects the clinical variables. It is therefore advisable to carefully assess the use of this information (both the MBDS directly as well as its grouping through the use of patient classification systems), and the indicators derived from it as its quality is not guaranteed. Systematic assessment and quality control of the MBDS production is advised.