Uterine leiomyoma is the most common tumor in women of reproductive age, but rarely does it lead to fatal hemoperitoneum. We present an autopsy case in which the cause of death was massive hemoperitoneum due to rupture of a subserosal vein overlying a uterine leiomyoma. We report the case of a 28-year-old Japanese woman who had tuberous sclerosis and was gravida 0, para 0. She had a uterine leiomyoma leading to dysmenorrhea. Autopsy revealed a pinhole-sized rupture of a subserosal vein superficial to the leiomyoma that resulted in fatal hemoperitoneum. Rupture of a subserosal vein overlying a uterine leiomyoma may cause sudden and unexpected death.