Current guidelines and review articles emphasize that clinicians should consider group A beta-hemolytic streptococcus in the diagnosis and management of patients with acute pharyngitis. Recent data suggest that in adolescents and young adults (persons aged 15 to 24 years), Fusobacterium necrophorum causes endemic pharyngitis at a rate similar to that of group A beta-hemolytic streptococcus. On the basis of published epidemiologic data, F. necrophorum is estimated to cause the Lemierre syndrome-a life-threatening suppurative complication-at a higher incidence than that at which group A streptococcus causes acute rheumatic fever. Moreover, these estimates suggest greater morbidity and mortality from the Lemierre syndrome. The diagnostic paradigm for adolescent pharyngitis should therefore be expanded to consider F. necrophorum in addition to group A streptococcus. Expanding the pharyngitis paradigm will have several important implications. Further epidemiologic research is needed on both F. necrophorum pharyngitis (especially clinical presentation) and the Lemierre syndrome. Clinicians need reliable diagnostic techniques for F. necrophorum pharyngitis. In the meantime, adolescents and young adults who develop bacteremic symptoms should be aggressively treated with antibiotics for F. necrophorum infection. Physicians should avoid macrolides if they choose to treat streptococcus-negative pharyngitis empirically. Finally, pediatricians, internists, family physicians, and emergency department physicians should know the red flags for adolescent and young adult pharyngitis: worsening symptoms or neck swelling (especially unilateral neck swelling). Adolescent and young adult pharyngitis is more complicated than previously considered.