We report a case of Streptococcus pyogenes, β-hemolytic Streptococcus, Lancefield group A vulvovaginitis in an otherwise healthy adult female patient experiencing lactational amenorrhea. Group A streptococcal infection is the infective cause of vulvovaginitis in 21% of prepubescent girls, but it is an uncommon cause of vulvovaginitis in adults. Group A streptococcal vulvovaginitis is frequently associated with households that have had a recent outbreak of respiratory or dermal infection. The case described here appears to be unusual in that it was sexually transmitted, and the lack of estrogen associated with anovualtion may have been a predisposing factor for this unusual sexually transmitted disease. © 2008 by the Infectious Diseases Society of America. All rights reserved.