Two urogenital sinus syndromes. Interstitial cystitis and focal vulvitis. Forty-six young women had unusual and presumably noninfectious disorders of unknown etiology involving tissues derived from the embryonic urogenital sinus (urogenital sinus syndromes). Ten women had interstitial cystitis, and 25 had focal vulvitis. Eleven women had both interstitial cystitis and focal vulvitis. The affected groups were similar in demographic and other characteristics. Most were white and in their mid-20s. Both unusual conditions occurred in the same woman more often than could be expected by chance. This observation suggests that some common, perhaps autoimmune mechanism may be involved in the etiology of these syndromes. 