Statement of Problem: As the duration of hospital stay could be an indicator of the severity of infection (Including odontogenic sources); defining related variables could be very helpful in the treatment process. All clinical and paraclinical variables related to sever head and neck infections of odontogenic origin have not been fully evaluated.Purpose: This study was designed to identify the potential risk factors associated with increasing hospital stay in patients with deep head and neck spaces infections of odontogenic origin.Materials and Method: A total of 297 patients admitted to Shiraz Khalili hospital (1996-2006) with head and neck spaces infection were retrospectively identified by a medical chart view. Data concerning patient demographics, source and location of infection, culture results, and treatment modalities were evaluated. Linear regression techniques were used to explain the relationship between patient admission characteristics and duration of hospitalization.Results: A total of 34.3 % (n=102) of the patients had head and neck spaces infections of odontogenic origin. The most common location of infection was submandibular space (32%), followed by masseter space (22%) and Ludwig’s angina (20%). Culture results showed non-hemolytic streptococcus as the most common microorganism with the prevalence of 61.6%.The most frequent signs and symptoms were swelling and pain. The results showed a higher percentage of hospital admissions for the middle socioeconomic status (58.8%). Variables such as high weight, blood sodium level less than 135, preexisting disease and increasing in blood mean cell volume (MCV) were associated with longer hospital stay. Only 1 (0.9%) death was reported as the result of these infections.Conclusion: Odontogenic infections were a common source of deep head and neck spaces infection resulted in longer hospital stay. Paying particular attention to the variables that lead to longer hospital stay could be very important in formulating the treatment plan and reducing complications.