A 20-year-old woman was referred to our hospital for further evaluation on persistent pyuria. Physical examination showed a tender solid suprapubic mass. Computed tomography showed a right ovarian multilocular cystic tumor just above the urinary bladder. Cystoscopy showed pus leakage from an orifice in a hemisphere protrusion of the bladder wall. A small catheter could be inserted into the orifice. It revealed a fistula 4 cm in length between the right ovarian tumor and the vesical cavity. The tumor and the adjacent thickened bladder wall with an abscess and fistula were resected en bloc. Also a small left ovarian cyst was enucleated. Histopathological examination showed bilateral ovarian dermoid cysts, abscess formation, and marked inflammatory change around the fistula in the vesical wall. The fistula was thought to be the consequence of infection of the ovarian cyst.