Objectives: A retrospective study is made of the odontogenic infections treated in La Paz University Hospital (Madrid, Spain) during 2007 and 2008, with an epidemiological and microbiological analysis of a large group of patients.Study Design: A retrospective descriptive study was made, involving the consecutive inclusion of all patients with odontogenic infection requiring admission to our hospital in the period between January 2007 and December 2008. Results: A total of 151 patients were included, with a mean age of 40.3 years and a balanced gender distribution. The most frequently affected teeth were those located in the posterior mandibular segments, caries being the main underlying cause. Most isolates comprised mixed flora, particularly viridans streptococci, different species of Prevotella, Micromonas micros, and different species of Actinomyces. Susceptibility analysis of the microbial isolates showed a high percentage resistance to clindamycin (42.8% of all isolates), particularly among viridans streptococci.Conclusions: The use of antibiotics in head and neck infections requires updated protocols based not only on the existing scientific evidence but also on the epidemiological reality of each center. On the other hand, identification is required of the surgical factors determining infection and how they influence morbidity associated with this type of pathology. © Medicina Oral.