Chlamydia pneumoniae has recently been shown to be a cause of pharyngitis. Because the impact of this pathogen on United States Air Force basic trainees is unknown, the authors undertook a prospective study to evaluate the prevalence of C pneumoniae. Of 118 asymptomatic basic trainees, 43% had preexisting antibodies to C pneumoniae and 0.9% had serologic evidence of C pneumoniae infection. Of 226 symptomatic basic trainees, only four (1.8%) met the criteria for serologic evidence of acute C pneumoniae infection. No other cause of pharyngitis was found in three of four of these basic trainees. Three of the trainees with C pneumoniae infection had hoarseness and all had a dry cough. All symptoms resolved without specific antichlamydial therapy. Chlamydia pneumoniae was an uncommon cause of pharyngitis in basic trainees, appearing as a mild, self-limiting illness.