erythrasma is an uncommon vulvar infection best diagnosed by its fluorescence under the wood lamp this report shows that despite a negative wood lamp examination the diagnosis can be made histologically a 42 year old woman was referred to our clinic with a persistent candidal infection evaluation included a wood lamp examination wet mount and potassium hydroxide test of the affected skin all of which were negative a biopsy of the area demonstrated rods and filamentous organisms in the keratotic layer consistent with a corynebacterium minutissimum infection the patient was diagnosed as having erythrasma and she responded to oral erythromycin persistent vulvar diseases may be caused by erythrasma despite a negative wood lamp examination the diagnosis can be made by biopsy of the lesion.