Acute pharyngitis is one of the most common illnesses for which patients visit primary care physicians. Most cases are of viral origin, and with few exceptions these illnesses are both benign and self-limited. The most important bacterial cause is the beta-hemolytic group A streptococcus. There are other uncommon or rare types of pharyngitis. For some of these treatment is required or available, and some may be life threatening. Among those discussed in this article are diphtheria, gonorrhea, HIV infection, peritonsillar abscess, and epiglottitis.