We describe a case of acute erosive vulvovaginitis accompanying Borrelia burgdorferi infection. The patient is a 57-year-old woman previously diagnosed with Lyme disease who presented with a painful erosive genital lesion. At the time of the outbreak, she was being treated with oral antibiotics, and she tested serologically positive for B burgdorferi and serologically negative for syphilis. Histological examination of biopsy tissue from the lesion was not characteristic of dermatopathological patterns typical of erosive vulvar conditions. Dieterle-stained biopsy sections revealed visible spirochetes throughout the stratum spinosum and stratum basale, and anti- B burgdorferi immunostaining was positive. Motile spirochetes were observed by darkfield microscopy and cultured in Barbour-Stoner-Kelly-complete medium inoculated with skin scrapings from the lesion. Cultured spirochetes were identified genetically as B burgdorferi sensu stricto by polymerase chain reaction, while polymerase chain reaction amplification of treponemal gene targets was negative. The condition resolved after treatment with additional systemic antibiotic therapy and topical antibiotics. In cases of genital ulceration that have no identifiable etiology, the possibility of B burgdorferi spirochetal infection should be considered.