A previously healthy 22-year-old man acquired tonsillitis due to Streptococcus equisimilis, a group C Streptococcus. He rapidly developed pneumonia, empyema, septicemia, and metastatic arthritis, and despite appropriate therapy with antibiotics and drainage of abscesses, he experienced progressive respiratory insufficiency and died. The four species of group C streptococci are described in terms of their biochemical properties, the infections they cause in animals, and their tendency to produce disease in humans. Pharyngeal carriage of these organisms is not rare, and outbreaks of pharyngitis and tonsillitis occur. Group C streptococcal pneumonia, like group A pneumonia, is often a severe disease with a prolonged febrile course and frequently is complicated by empyema. Appropriate management includes isolation of the patient, penicillin G therapy, drainage, and respiratory support.