In young adults with acute pharyngitis, the main differential diagnosis is between GAS pharyngitis, EBV infectious mononucleosis, or other causes of viral pharyngitis. A positive RST does not differentiate GAS colonization from infection as is well illustrated by this case. Laboratory test results must be interpreted in the appropriate clinical context to be diagnostically meaningful. The RST only detects group A streptococci, but does not, of itself, implicate a causative role in the patient's pharyngitis. Without clinical correlation based on the clinical findings of GAS pharyngitis a positive RST may mislead the unwary physician to unnecessarily treat colonization rather than infection. I report an interesting case of a young adult who presented to the ED with no fever and acute pharyngitis. His RST was positive, and he was treated with procaine penicillin and released. Three days later he was re-admitted to the hospital with severe Herpes gingivostomatitis.