Septic arthritis of the shoulder girdle remains relatively uncommon, with Staphylococcus aureus and β-hemolytic streptococci the typical offending organisms in adult patients. Rare cases of Streptococcus viridans, an oral bacterium with low virulence, have been reported in the setting of septic arthritis, mostly involving the knee joint or the sternoclavicular joint. In this article, we report a case of Streptococcus mitis infection of the glenohumeral joint that likely resulted from hematogenous spread after oral trauma in a patient with poor underlying dentition. Prompt diagnosis followed by arthroscopic irrigation and débridement of the glenohumeral joint resulted in a satisfactory clinical outcome.