A case of mirror syndrome is described in a 16-year-old patient with a 22-week pregnancy who presented with severe abdominal pain. Fetal ultrasonography showed the presence of a single cephalic fetus, a large amount of fluid in the fetal abdominal and thoracic cavities, placental edema, polyhydramnios and a cystic tumor in the sacral region. The newborn showed subcutaneous edema with scarce pleural and pericardial fluid and a tumor compatible with fetal sacrococcygeal teratoma.